clickhousedb_deparse.c

/*-------------------------------------------------------------------------
 *
 * clickhousedb_deparse.c
 *		  Query deparser for clickhousedb_fdw
 *
 * Portions Copyright (c) 2012-2019, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *		  contrib/postgres_fdw/clickhousedb_deparse.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "lib/clickhouse-client.h"
#include "clickhousedb_fdw.h"

#include "access/heapam.h"
#include "access/htup_details.h"
#include "access/sysattr.h"
#include "catalog/pg_aggregate.h"
#include "catalog/pg_collation.h"
#include "catalog/pg_namespace.h"
#include "catalog/pg_operator.h"
#include "catalog/pg_proc.h"
#include "catalog/pg_type.h"
#include "commands/defrem.h"
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#include "nodes/plannodes.h"
#include "optimizer/clauses.h"
#include "optimizer/prep.h"
#include "optimizer/tlist.h"
#include "optimizer/var.h"
#include "parser/parsetree.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"
#include "utils/rel.h"
#include "utils/syscache.h"
#include "utils/typcache.h"


/*
 * Global context for foreign_expr_walker's search of an expression tree.
 */
typedef struct foreign_glob_cxt
{
        PlannerInfo *root;			/* global planner state */
        RelOptInfo *foreignrel;		/* the foreign relation we are planning for */
        Relids		relids;			/* relids of base relations in the underlying
						 * scan */
} foreign_glob_cxt;

/*
 * Local (per-tree-level) context for foreign_expr_walker's search.
 * This is concerned with identifying collations used in the expression.
 */
typedef enum
{
        FDW_COLLATE_NONE,			/* expression is of a noncollatable type, or
						 * it has default collation that is not
						 * traceable to a foreign Var */
        FDW_COLLATE_SAFE,			/* collation derives from a foreign Var */
        FDW_COLLATE_UNSAFE			/* collation is non-default and derives from
						 * something other than a foreign Var */
} FDWCollateState;

typedef struct foreign_loc_cxt
{
        Oid			collation;		/* OID of current collation, if any */
        FDWCollateState state;		/* state of current collation choice */
} foreign_loc_cxt;

/*
 * Context for deparseExpr
 */
typedef struct deparse_expr_cxt
{
        PlannerInfo *root;			/* global planner state */
        RelOptInfo *foreignrel;		/* the foreign relation we are planning for */
        RelOptInfo *scanrel;		/* the underlying scan relation. Same as
					 * foreignrel, when that represents a join or
					 * a base relation. */
        StringInfo	buf;			/* output buffer to append to */
        List	  **params_list;	/* exprs that will become remote Params */
} deparse_expr_cxt;

#define REL_ALIAS_PREFIX	"r"
/* Handy macro to add relation name qualification */
#define ADD_REL_QUALIFIER(buf, varno)	\
        appendStringInfo((buf), "%s%d.", REL_ALIAS_PREFIX, (varno))
#define SUBQUERY_REL_ALIAS_PREFIX	"s"
#define SUBQUERY_COL_ALIAS_PREFIX	"c"

/*
 * Functions to determine whether an expression can be evaluated safely on
 * remote server.
 */
static bool foreign_expr_walker(Node *node,
                                foreign_glob_cxt *glob_cxt,
                                foreign_loc_cxt *outer_cxt);
static char *deparse_type_name(Oid type_oid, int32 typemod);

/*
 * Functions to construct string representation of a node tree.
 */
static void deparseTargetList(StringInfo buf,
                              RangeTblEntry *rte,
                              Index rtindex,
                              Relation rel,
                              bool is_returning,
                              Bitmapset *attrs_used,
                              bool qualify_col,
                              List **retrieved_attrs);
static void deparseExplicitTargetList(List *tlist,
                                      bool is_returning,
                                      List **retrieved_attrs,
                                      deparse_expr_cxt *context);
static void deparseSubqueryTargetList(deparse_expr_cxt *context);
static void deparseReturningList(StringInfo buf, RangeTblEntry *rte,
                                 Index rtindex, Relation rel,
                                 bool trig_after_row,
                                 List *returningList,
                                 List **retrieved_attrs);
static void deparseColumnRef(StringInfo buf, int varno, int varattno,
                             RangeTblEntry *rte, bool qualify_col);
static void deparseRelation(StringInfo buf, Relation rel);
static void deparseExpr(Expr *expr, deparse_expr_cxt *context);
static void deparseVar(Var *node, deparse_expr_cxt *context);
static void deparseConst(Const *node, deparse_expr_cxt *context, int showtype);
static void deparseParam(Param *node, deparse_expr_cxt *context);
static void deparseArrayRef(ArrayRef *node, deparse_expr_cxt *context);
static void deparseFuncExpr(FuncExpr *node, deparse_expr_cxt *context);
static void deparseOpExpr(OpExpr *node, deparse_expr_cxt *context);
static void deparseOperatorName(StringInfo buf, Form_pg_operator opform);
static void deparseDistinctExpr(DistinctExpr *node, deparse_expr_cxt *context);
static void deparseScalarArrayOpExpr(ScalarArrayOpExpr *node,
                                     deparse_expr_cxt *context);
static void deparseRelabelType(RelabelType *node, deparse_expr_cxt *context);
static void deparseBoolExpr(BoolExpr *node, deparse_expr_cxt *context);
static void deparseNullTest(NullTest *node, deparse_expr_cxt *context);
static void deparseArrayExpr(ArrayExpr *node, deparse_expr_cxt *context);
static void printRemoteParam(int paramindex, Oid paramtype, int32 paramtypmod,
                             deparse_expr_cxt *context);
static void printRemotePlaceholder(Oid paramtype, int32 paramtypmod,
                                   deparse_expr_cxt *context);
static void deparseSelectSql(List *tlist, bool is_subquery,
                             List **retrieved_attrs,
                             deparse_expr_cxt *context);
static void deparseLockingClause(deparse_expr_cxt *context);
static void appendOrderByClause(List *pathkeys, deparse_expr_cxt *context);
static void appendConditions(List *exprs, deparse_expr_cxt *context);
static void deparseFromExprForRel(StringInfo buf, PlannerInfo *root,
                                  RelOptInfo *foreignrel, bool use_alias,
                                  Index ignore_rel, List **ignore_conds,
                                  List **params_list);
static void deparseFromExpr(List *quals, deparse_expr_cxt *context);
static void deparseRangeTblRef(StringInfo buf, PlannerInfo *root,
                               RelOptInfo *foreignrel, bool make_subquery,
                               Index ignore_rel, List **ignore_conds, List **params_list);
static void deparseAggref(Aggref *node, deparse_expr_cxt *context);
static void appendGroupByClause(List *tlist, deparse_expr_cxt *context);
static void appendAggOrderBy(List *orderList, List *targetList,
                             deparse_expr_cxt *context);
static void appendFunctionName(Oid funcid, deparse_expr_cxt *context);
static Node *deparseSortGroupClause(Index ref, List *tlist, bool force_colno,
                                    deparse_expr_cxt *context);

/*
 * Helper functions
 */
static bool is_subquery_var(Var *node, RelOptInfo *foreignrel,
                            int *relno, int *colno);
static void get_relation_column_alias_ids(Var *node, RelOptInfo *foreignrel,
                int *relno, int *colno);


/*
 * Examine each qual clause in input_conds, and classify them into two groups,
 * which are returned as two lists:
 *	- remote_conds contains expressions that can be evaluated remotely
 *	- local_conds contains expressions that can't be evaluated remotely
 */
void
classifyConditions(PlannerInfo *root,
                   RelOptInfo *baserel,
                   List *input_conds,
                   List **remote_conds,
                   List **local_conds)
{
        ListCell   *lc;

        *remote_conds = NIL;
        *local_conds = NIL;

        foreach (lc, input_conds)
        {
                RestrictInfo *ri = lfirst_node(RestrictInfo, lc);

                if (is_foreign_expr(root, baserel, ri->clause))
                {
                        *remote_conds = lappend(*remote_conds, ri);
                }
                else
                {
                        *local_conds = lappend(*local_conds, ri);
                }
        }
}

/*
 * Returns true if given expr is safe to evaluate on the foreign server.
 */
bool
is_foreign_expr(PlannerInfo *root,
                RelOptInfo *baserel,
                Expr *expr)
{
        foreign_glob_cxt glob_cxt;
        foreign_loc_cxt loc_cxt;
        CHFdwRelationInfo *fpinfo = (CHFdwRelationInfo *)(baserel->fdw_private);

        /*
         * Check that the expression consists of nodes that are safe to execute
         * remotely.
         */
        glob_cxt.root = root;
        glob_cxt.foreignrel = baserel;

        /*
         * For an upper relation, use relids from its underneath scan relation,
         * because the upperrel's own relids currently aren't set to anything
         * meaningful by the core code.  For other relation, use their own relids.
         */
        if (IS_UPPER_REL(baserel))
        {
                glob_cxt.relids = fpinfo->outerrel->relids;
        }
        else
        {
                glob_cxt.relids = baserel->relids;
        }
        loc_cxt.collation = InvalidOid;
        loc_cxt.state = FDW_COLLATE_NONE;
        if (!foreign_expr_walker((Node *) expr, &glob_cxt, &loc_cxt))
        {
                return false;
        }

        /*
         * If the expression has a valid collation that does not arise from a
         * foreign var, the expression can not be sent over.
         */
        if (loc_cxt.state == FDW_COLLATE_UNSAFE)
        {
                return false;
        }

        /*
         * An expression which includes any mutable functions can't be sent over
         * because its result is not stable.  For example, sending now() remote
         * side could cause confusion from clock offsets.  Future versions might
         * be able to make this choice with more granularity.  (We check this last
         * because it requires a lot of expensive catalog lookups.)
         */
        if (contain_mutable_functions((Node *) expr))
        {
                return false;
        }

        /* OK to evaluate on the remote server */
        return true;
}

/*
 * Check if expression is safe to execute remotely, and return true if so.
 *
 * In addition, *outer_cxt is updated with collation information.
 *
 * We must check that the expression contains only node types we can deparse,
 * that all types/functions/operators are safe to send (they are "shippable"),
 * and that all collations used in the expression derive from Vars of the
 * foreign table.  Because of the latter, the logic is pretty close to
 * assign_collations_walker() in parse_collate.c, though we can assume here
 * that the given expression is valid.  Note function mutability is not
 * currently considered here.
 */
static bool
foreign_expr_walker(Node *node,
                    foreign_glob_cxt *glob_cxt,
                    foreign_loc_cxt *outer_cxt)
{
        bool		check_type = true;
        CHFdwRelationInfo *fpinfo;
        foreign_loc_cxt inner_cxt;
        Oid			collation;
        FDWCollateState state;

        /* Need do nothing for empty subexpressions */
        if (node == NULL)
        {
                return true;
        }

        /* May need server info from baserel's fdw_private struct */
        fpinfo = (CHFdwRelationInfo *)(glob_cxt->foreignrel->fdw_private);

        /* Set up inner_cxt for possible recursion to child nodes */
        inner_cxt.collation = InvalidOid;
        inner_cxt.state = FDW_COLLATE_NONE;

        switch (nodeTag(node))
        {
                case T_Var:
                {
                        Var		   *var = (Var *) node;

                        /*
                         * If the Var is from the foreign table, we consider its
                         * collation (if any) safe to use.  If it is from another
                         * table, we treat its collation the same way as we would a
                         * Param's collation, ie it's not safe for it to have a
                         * non-default collation.
                         */
                        if (bms_is_member(var->varno, glob_cxt->relids) &&
                                        var->varlevelsup == 0)
                        {
                                /* Var belongs to foreign table */

                                /*
                                 * System columns other than ctid and oid should not be
                                 * sent to the remote, since we don't make any effort to
                                 * ensure that local and remote values match (tableoid, in
                                 * particular, almost certainly doesn't match).
                                 */
                                if (var->varattno < 0 &&
                                                var->varattno != SelfItemPointerAttributeNumber &&
                                                var->varattno != ObjectIdAttributeNumber)
                                {
                                        return false;
                                }

                                /* Else check the collation */
                                collation = var->varcollid;
                                state = OidIsValid(collation) ? FDW_COLLATE_SAFE : FDW_COLLATE_NONE;
                        }
                        else
                        {
                                /* Var belongs to some other table */
                                collation = var->varcollid;
                                if (collation == InvalidOid ||
                                                collation == DEFAULT_COLLATION_OID)
                                {
                                        /*
                                         * It's noncollatable, or it's safe to combine with a
                                         * collatable foreign Var, so set state to NONE.
                                         */
                                        state = FDW_COLLATE_NONE;
                                }
                                else
                                {
                                        /*
                                         * Do not fail right away, since the Var might appear
                                         * in a collation-insensitive context.
                                         */
                                        state = FDW_COLLATE_UNSAFE;
                                }
                        }
                }
                break;
                case T_Const:
                {
                        Const	   *c = (Const *) node;

                        /*
                         * If the constant has nondefault collation, either it's of a
                         * non-builtin type, or it reflects folding of a CollateExpr.
                         * It's unsafe to send to the remote unless it's used in a
                         * non-collation-sensitive context.
                         */
                        collation = c->constcollid;
                        if (collation == InvalidOid ||
                                        collation == DEFAULT_COLLATION_OID)
                        {
                                state = FDW_COLLATE_NONE;
                        }
                        else
                        {
                                state = FDW_COLLATE_UNSAFE;
                        }
                }
                break;
                case T_Param:
                {
                        /* We are not supporting param push down*/
                        return false;
                }
                break;
                case T_ArrayRef:
                {
                        ArrayRef   *ar = (ArrayRef *) node;

                        /* Assignment should not be in restrictions. */
                        if (ar->refassgnexpr != NULL)
                        {
                                return false;
                        }

                        /*
                         * Recurse to remaining subexpressions.  Since the array
                         * subscripts must yield (noncollatable) integers, they won't
                         * affect the inner_cxt state.
                         */
                        if (!foreign_expr_walker((Node *) ar->refupperindexpr,
                                                 glob_cxt, &inner_cxt))
                        {
                                return false;
                        }
                        if (!foreign_expr_walker((Node *) ar->reflowerindexpr,
                                                 glob_cxt, &inner_cxt))
                        {
                                return false;
                        }
                        if (!foreign_expr_walker((Node *) ar->refexpr,
                                                 glob_cxt, &inner_cxt))
                        {
                                return false;
                        }

                        /*
                         * Array subscripting should yield same collation as input,
                         * but for safety use same logic as for function nodes.
                         */
                        collation = ar->refcollid;
                        if (collation == InvalidOid)
                        {
                                state = FDW_COLLATE_NONE;
                        }
                        else if (inner_cxt.state == FDW_COLLATE_SAFE &&
                                        collation == inner_cxt.collation)
                        {
                                state = FDW_COLLATE_SAFE;
                        }
                        else if (collation == DEFAULT_COLLATION_OID)
                        {
                                state = FDW_COLLATE_NONE;
                        }
                        else
                        {
                                state = FDW_COLLATE_UNSAFE;
                        }
                }
                break;
                case T_FuncExpr:
                {
                        FuncExpr   *fe = (FuncExpr *) node;

                        /*
                         * If function used by the expression is not shippable, it
                         * can't be sent to remote because it might have incompatible
                         * semantics on remote side.
                         */
                        if (!is_shippable(fe->funcid, ProcedureRelationId, fpinfo))
                        {
                                return false;
                        }

                        /*
                         * Recurse to input subexpressions.
                         */
                        if (!foreign_expr_walker((Node *) fe->args,
                                                 glob_cxt, &inner_cxt))
                        {
                                return false;
                        }

                        /*
                         * If function's input collation is not derived from a foreign
                         * Var, it can't be sent to remote.
                         */
                        if (fe->inputcollid == InvalidOid)
                                /* OK, inputs are all noncollatable */ ;
                        else if (inner_cxt.state != FDW_COLLATE_SAFE ||
                                        fe->inputcollid != inner_cxt.collation)
                        {
                                return false;
                        }

                        /*
                         * Detect whether node is introducing a collation not derived
                         * from a foreign Var.  (If so, we just mark it unsafe for now
                         * rather than immediately returning false, since the parent
                         * node might not care.)
                         */
                        collation = fe->funccollid;
                        if (collation == InvalidOid)
                        {
                                state = FDW_COLLATE_NONE;
                        }
                        else if (inner_cxt.state == FDW_COLLATE_SAFE &&
                                        collation == inner_cxt.collation)
                        {
                                state = FDW_COLLATE_SAFE;
                        }
                        else if (collation == DEFAULT_COLLATION_OID)
                        {
                                state = FDW_COLLATE_NONE;
                        }
                        else
                        {
                                state = FDW_COLLATE_UNSAFE;
                        }
                }
                break;
                case T_OpExpr:
                case T_DistinctExpr:	/* struct-equivalent to OpExpr */
                {
                        OpExpr	   *oe = (OpExpr *) node;

                        /*
                         * Similarly, only shippable operators can be sent to remote.
                         * (If the operator is shippable, we assume its underlying
                         * function is too.)
                         */
                        if (!is_shippable(oe->opno, OperatorRelationId, fpinfo))
                        {
                                return false;
                        }

                        /*
                         * Recurse to input subexpressions.
                         */
                        if (!foreign_expr_walker((Node *) oe->args,
                                                 glob_cxt, &inner_cxt))
                        {
                                return false;
                        }

                        /*
                         * If operator's input collation is not derived from a foreign
                         * Var, it can't be sent to remote.
                         */
                        if (oe->inputcollid == InvalidOid)
                                /* OK, inputs are all noncollatable */ ;
                        else if (inner_cxt.state != FDW_COLLATE_SAFE ||
                                        oe->inputcollid != inner_cxt.collation)
                        {
                                return false;
                        }

                        /* Result-collation handling is same as for functions */
                        collation = oe->opcollid;
                        if (collation == InvalidOid)
                        {
                                state = FDW_COLLATE_NONE;
                        }
                        else if (inner_cxt.state == FDW_COLLATE_SAFE &&
                                        collation == inner_cxt.collation)
                        {
                                state = FDW_COLLATE_SAFE;
                        }
                        else if (collation == DEFAULT_COLLATION_OID)
                        {
                                state = FDW_COLLATE_NONE;
                        }
                        else
                        {
                                state = FDW_COLLATE_UNSAFE;
                        }
                }
                break;
                case T_ScalarArrayOpExpr:
                {
                    /* Don't push-down the scalar expression because clickhouse does not support that. */
                    return false;
                }
                break;
                case T_RelabelType:
                {
                        RelabelType *r = (RelabelType *) node;

                        /*
                         * Recurse to input subexpression.
                         */
                        if (!foreign_expr_walker((Node *) r->arg,
                                                 glob_cxt, &inner_cxt))
                        {
                                return false;
                        }

                        /*
                         * RelabelType must not introduce a collation not derived from
                         * an input foreign Var (same logic as for a real function).
                         */
                        collation = r->resultcollid;
                        if (collation == InvalidOid)
                        {
                                state = FDW_COLLATE_NONE;
                        }
                        else if (inner_cxt.state == FDW_COLLATE_SAFE &&
                                        collation == inner_cxt.collation)
                        {
                                state = FDW_COLLATE_SAFE;
                        }
                        else if (collation == DEFAULT_COLLATION_OID)
                        {
                                state = FDW_COLLATE_NONE;
                        }
                        else
                        {
                                state = FDW_COLLATE_UNSAFE;
                        }
                }
                break;
                case T_BoolExpr:
                {
                        BoolExpr   *b = (BoolExpr *) node;

                        /*
                         * Recurse to input subexpressions.
                         */
                        if (!foreign_expr_walker((Node *) b->args,
                                                 glob_cxt, &inner_cxt))
                        {
                                return false;
                        }

                        /* Output is always boolean and so noncollatable. */
                        collation = InvalidOid;
                        state = FDW_COLLATE_NONE;
                }
                break;
                case T_NullTest:
                {
                        NullTest   *nt = (NullTest *) node;

                        /*
                         * Recurse to input subexpressions.
                         */
                        if (!foreign_expr_walker((Node *) nt->arg,
                                                 glob_cxt, &inner_cxt))
                        {
                                return false;
                        }

                        /* Output is always boolean and so noncollatable. */
                        collation = InvalidOid;
                        state = FDW_COLLATE_NONE;
                }
                break;
                case T_ArrayExpr:
                {
                        ArrayExpr  *a = (ArrayExpr *) node;

                        /*
                         * Recurse to input subexpressions.
                         */
                        if (!foreign_expr_walker((Node *) a->elements,
                                                 glob_cxt, &inner_cxt))
                        {
                                return false;
                        }

                        /*
                         * ArrayExpr must not introduce a collation not derived from
                         * an input foreign Var (same logic as for a function).
                         */
                        collation = a->array_collid;
                        if (collation == InvalidOid)
                        {
                                state = FDW_COLLATE_NONE;
                        }
                        else if (inner_cxt.state == FDW_COLLATE_SAFE &&
                                        collation == inner_cxt.collation)
                        {
                                state = FDW_COLLATE_SAFE;
                        }
                        else if (collation == DEFAULT_COLLATION_OID)
                        {
                                state = FDW_COLLATE_NONE;
                        }
                        else
                        {
                                state = FDW_COLLATE_UNSAFE;
                        }
                }
                break;
                case T_List:
                {
                        List	   *l = (List *) node;
                        ListCell   *lc;

                        /*
                         * Recurse to component subexpressions.
                         */
                        foreach (lc, l)
                        {
                                if (!foreign_expr_walker((Node *) lfirst(lc),
                                                         glob_cxt, &inner_cxt))
                                {
                                        return false;
                                }
                        }

                        /*
                         * When processing a list, collation state just bubbles up
                         * from the list elements.
                         */
                        collation = inner_cxt.collation;
                        state = inner_cxt.state;

                        /* Don't apply exprType() to the list. */
                        check_type = false;
                }
                break;
                case T_Aggref:
                {
                        Aggref	   *agg = (Aggref *) node;
                        ListCell   *lc;

                        /* Not safe to pushdown when not in grouping context */
                        if (!IS_UPPER_REL(glob_cxt->foreignrel))
                        {
                                return false;
                        }

                        /* Only non-split aggregates are pushable. */
                        if (agg->aggsplit != AGGSPLIT_SIMPLE)
                        {
                                return false;
                        }

                        /* As usual, it must be shippable. */
                        if (!is_shippable(agg->aggfnoid, ProcedureRelationId, fpinfo))
                        {
                                return false;
                        }

                        /*
                         * Recurse to input args. aggdirectargs, aggorder and
                         * aggdistinct are all present in args, so no need to check
                         * their shippability explicitly.
                         */
                        foreach (lc, agg->args)
                        {
                                Node	   *n = (Node *) lfirst(lc);

                                /* If TargetEntry, extract the expression from it */
                                if (IsA(n, TargetEntry))
                                {
                                        TargetEntry *tle = (TargetEntry *) n;

                                        n = (Node *) tle->expr;
                                }

                                if (!foreign_expr_walker(n, glob_cxt, &inner_cxt))
                                {
                                        return false;
                                }
                        }

                        /*
                         * For aggorder elements, check whether the sort operator, if
                         * specified, is shippable or not.
                         */
                        if (agg->aggorder)
                        {
                                ListCell   *lc;

                                foreach (lc, agg->aggorder)
                                {
                                        SortGroupClause *srt = (SortGroupClause *) lfirst(lc);
                                        Oid			sortcoltype;
                                        TypeCacheEntry *typentry;
                                        TargetEntry *tle;

                                        tle = get_sortgroupref_tle(srt->tleSortGroupRef,
                                                                   agg->args);
                                        sortcoltype = exprType((Node *) tle->expr);
                                        typentry = lookup_type_cache(sortcoltype,
                                                                     TYPECACHE_LT_OPR | TYPECACHE_GT_OPR);
                                        /* Check shippability of non-default sort operator. */
                                        if (srt->sortop != typentry->lt_opr &&
                                                        srt->sortop != typentry->gt_opr &&
                                                        !is_shippable(srt->sortop, OperatorRelationId,
                                                                      fpinfo))
                                        {
                                                return false;
                                        }
                                }
                        }

                        /* Check aggregate filter */
                        if (!foreign_expr_walker((Node *) agg->aggfilter,
                                                 glob_cxt, &inner_cxt))
                        {
                                return false;
                        }

                        /*
                         * If aggregate's input collation is not derived from a
                         * foreign Var, it can't be sent to remote.
                         */
                        if (agg->inputcollid == InvalidOid)
                                /* OK, inputs are all noncollatable */ ;
                        else if (inner_cxt.state != FDW_COLLATE_SAFE ||
                                        agg->inputcollid != inner_cxt.collation)
                        {
                                return false;
                        }

                        /*
                         * Detect whether node is introducing a collation not derived
                         * from a foreign Var.  (If so, we just mark it unsafe for now
                         * rather than immediately returning false, since the parent
                         * node might not care.)
                         */
                        collation = agg->aggcollid;
                        if (collation == InvalidOid)
                        {
                                state = FDW_COLLATE_NONE;
                        }
                        else if (inner_cxt.state == FDW_COLLATE_SAFE &&
                                        collation == inner_cxt.collation)
                        {
                                state = FDW_COLLATE_SAFE;
                        }
                        else if (collation == DEFAULT_COLLATION_OID)
                        {
                                state = FDW_COLLATE_NONE;
                        }
                        else
                        {
                                state = FDW_COLLATE_UNSAFE;
                        }
                }
                break;
                default:

                        /*
                         * If it's anything else, assume it's unsafe.  This list can be
                         * expanded later, but don't forget to add deparse support below.
                         */
                        return false;
        }

        /*
         * If result type of given expression is not shippable, it can't be sent
         * to remote because it might have incompatible semantics on remote side.
         */
        if (check_type && !is_shippable(exprType(node), TypeRelationId, fpinfo))
        {
                return false;
        }

        /*
         * Now, merge my collation information into my parent's state.
         */
        if (state > outer_cxt->state)
        {
                /* Override previous parent state */
                outer_cxt->collation = collation;
                outer_cxt->state = state;
        }
        else if (state == outer_cxt->state)
        {
                /* Merge, or detect error if there's a collation conflict */
                switch (state)
                {
                        case FDW_COLLATE_NONE:
                                /* Nothing + nothing is still nothing */
                                break;
                        case FDW_COLLATE_SAFE:
                                if (collation != outer_cxt->collation)
                                {
                                        /*
                                         * Non-default collation always beats default.
                                         */
                                        if (outer_cxt->collation == DEFAULT_COLLATION_OID)
                                        {
                                                /* Override previous parent state */
                                                outer_cxt->collation = collation;
                                        }
                                        else if (collation != DEFAULT_COLLATION_OID)
                                        {
                                                /*
                                                 * Conflict; show state as indeterminate.  We don't
                                                 * want to "return false" right away, since parent
                                                 * node might not care about collation.
                                                 */
                                                outer_cxt->state = FDW_COLLATE_UNSAFE;
                                        }
                                }
                                break;
                        case FDW_COLLATE_UNSAFE:
                                /* We're still conflicted ... */
                                break;
                }
        }

        /* It looks OK */
        return true;
}

/*
 * Convert type OID + typmod info into a type name we can ship to the remote
 * server.  Someplace else had better have verified that this type name is
 * expected to be known on the remote end.
 *
 * This is almost just format_type_with_typemod(), except that if left to its
 * own devices, that function will make schema-qualification decisions based
 * on the local search_path, which is wrong.  We must schema-qualify all
 * type names that are not in pg_catalog.  We assume here that built-in types
 * are all in pg_catalog and need not be qualified; otherwise, qualify.
 */
static char *
deparse_type_name(Oid type_oid, int32 typemod)
{
        bits16		flags = FORMAT_TYPE_TYPEMOD_GIVEN;

        if (!is_builtin(type_oid))
        {
                flags |= FORMAT_TYPE_FORCE_QUALIFY;
        }

        return format_type_extended(type_oid, typemod, flags);
}

/*
 * Build the targetlist for given relation to be deparsed as SELECT clause.
 *
 * The output targetlist contains the columns that need to be fetched from the
 * foreign server for the given relation.  If foreignrel is an upper relation,
 * then the output targetlist can also contain expressions to be evaluated on
 * foreign server.
 */
List *
build_tlist_to_deparse(RelOptInfo *foreignrel)
{
        List	   *tlist = NIL;
        CHFdwRelationInfo *fpinfo = (CHFdwRelationInfo *) foreignrel->fdw_private;
        ListCell   *lc;

        /*
         * For an upper relation, we have already built the target list while
         * checking shippability, so just return that.
         */
        if (IS_UPPER_REL(foreignrel))
        {
                return fpinfo->grouped_tlist;
        }

        /*
         * We require columns specified in foreignrel->reltarget->exprs and those
         * required for evaluating the local conditions.
         */
        tlist = add_to_flat_tlist(tlist,
                                  pull_var_clause((Node *) foreignrel->reltarget->exprs,
                                                  PVC_RECURSE_PLACEHOLDERS));
        foreach (lc, fpinfo->local_conds)
        {
                RestrictInfo *rinfo = lfirst_node(RestrictInfo, lc);

                tlist = add_to_flat_tlist(tlist,
                                          pull_var_clause((Node *) rinfo->clause,
                                                          PVC_RECURSE_PLACEHOLDERS));
        }

        return tlist;
}

/*
 * Deparse SELECT statement for given relation into buf.
 *
 * tlist contains the list of desired columns to be fetched from foreign server.
 * For a base relation fpinfo->attrs_used is used to construct SELECT clause,
 * hence the tlist is ignored for a base relation.
 *
 * remote_conds is the list of conditions to be deparsed into the WHERE clause
 * (or, in the case of upper relations, into the HAVING clause).
 *
 * If params_list is not NULL, it receives a list of Params and other-relation
 * Vars used in the clauses; these values must be transmitted to the remote
 * server as parameter values.
 *
 * If params_list is NULL, we're generating the query for EXPLAIN purposes,
 * so Params and other-relation Vars should be replaced by dummy values.
 *
 * pathkeys is the list of pathkeys to order the result by.
 *
 * is_subquery is the flag to indicate whether to deparse the specified
 * relation as a subquery.
 *
 * List of columns selected is returned in retrieved_attrs.
 */
void
deparseSelectStmtForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *rel,
                        List *tlist, List *remote_conds, List *pathkeys,
                        bool is_subquery, List **retrieved_attrs,
                        List **params_list)
{
        deparse_expr_cxt context;
        CHFdwRelationInfo *fpinfo = (CHFdwRelationInfo *) rel->fdw_private;
        List	   *quals;

        elog(DEBUG2, "> %s:%d", __FUNCTION__, __LINE__);
        /*
         * We handle relations for foreign tables, joins between those and upper
         * relations.
         */
        Assert(IS_JOIN_REL(rel) || IS_SIMPLE_REL(rel) || IS_UPPER_REL(rel));

        /* Fill portions of context common to upper, join and base relation */
        context.buf = buf;
        context.root = root;
        context.foreignrel = rel;
        context.scanrel = IS_UPPER_REL(rel) ? fpinfo->outerrel : rel;
        context.params_list = params_list;

        /* Construct SELECT clause */
        deparseSelectSql(tlist, is_subquery, retrieved_attrs, &context);

        /*
         * For upper relations, the WHERE clause is built from the remote
         * conditions of the underlying scan relation; otherwise, we can use the
         * supplied list of remote conditions directly.
         */
        if (IS_UPPER_REL(rel))
        {
                CHFdwRelationInfo *ofpinfo;

                ofpinfo = (CHFdwRelationInfo *) fpinfo->outerrel->fdw_private;
                quals = ofpinfo->remote_conds;
        }
        else
        {
                quals = remote_conds;
        }

        /* Construct FROM and WHERE clauses */
        deparseFromExpr(quals, &context);

        if (IS_UPPER_REL(rel))
        {
                /* Append GROUP BY clause */
                appendGroupByClause(tlist, &context);

                /* Append HAVING clause */
                if (remote_conds)
                {
                        appendStringInfoString(buf, " HAVING ");
                        appendConditions(remote_conds, &context);
                }
        }

        /* Add ORDER BY clause if we found any useful pathkeys */
        if (pathkeys)
        {
                appendOrderByClause(pathkeys, &context);
        }

        /* Add any necessary FOR UPDATE/SHARE. */
        deparseLockingClause(&context);
        elog(DEBUG2, "> %s:%d", __FUNCTION__, __LINE__);
}

/*
 * Construct a simple SELECT statement that retrieves desired columns
 * of the specified foreign table, and append it to "buf".  The output
 * contains just "SELECT ... ".
 *
 * We also create an integer List of the columns being retrieved, which is
 * returned to *retrieved_attrs, unless we deparse the specified relation
 * as a subquery.
 *
 * tlist is the list of desired columns.  is_subquery is the flag to
 * indicate whether to deparse the specified relation as a subquery.
 * Read prologue of deparseSelectStmtForRel() for details.
 */
static void
deparseSelectSql(List *tlist, bool is_subquery, List **retrieved_attrs,
                 deparse_expr_cxt *context)
{
        StringInfo	buf = context->buf;
        RelOptInfo *foreignrel = context->foreignrel;
        PlannerInfo *root = context->root;
        CHFdwRelationInfo *fpinfo = (CHFdwRelationInfo *) foreignrel->fdw_private;

        elog(DEBUG2, "> %s:%d", __FUNCTION__, __LINE__);
        /*
         * Construct SELECT list
         */
        appendStringInfoString(buf, "SELECT ");

        if (is_subquery)
        {
                /*
                 * For a relation that is deparsed as a subquery, emit expressions
                 * specified in the relation's reltarget.  Note that since this is for
                 * the subquery, no need to care about *retrieved_attrs.
                 */
                deparseSubqueryTargetList(context);
        }
        else if (IS_JOIN_REL(foreignrel) || IS_UPPER_REL(foreignrel))
        {
                /*
                 * For a join or upper relation the input tlist gives the list of
                 * columns required to be fetched from the foreign server.
                 */
                deparseExplicitTargetList(tlist, false, retrieved_attrs, context);
        }
        else
        {
                /*
                 * For a base relation fpinfo->attrs_used gives the list of columns
                 * required to be fetched from the foreign server.
                 */
                RangeTblEntry *rte = planner_rt_fetch(foreignrel->relid, root);

                /*
                 * Core code already has some lock on each rel being planned, so we
                 * can use NoLock here.
                 */
                Relation	rel = heap_open(rte->relid, NoLock);

                deparseTargetList(buf, rte, foreignrel->relid, rel, false,
                                  fpinfo->attrs_used, false, retrieved_attrs);
                heap_close(rel, NoLock);
        }
        elog(DEBUG2, "< %s:%d", __FUNCTION__, __LINE__);
}

/*
 * Construct a FROM clause and, if needed, a WHERE clause, and append those to
 * "buf".
 *
 * quals is the list of clauses to be included in the WHERE clause.
 * (These may or may not include RestrictInfo decoration.)
 */
static void
deparseFromExpr(List *quals, deparse_expr_cxt *context)
{
        StringInfo	buf = context->buf;
        RelOptInfo *scanrel = context->scanrel;

        /* For upper relations, scanrel must be either a joinrel or a baserel */
        Assert(!IS_UPPER_REL(context->foreignrel) ||
               IS_JOIN_REL(scanrel) || IS_SIMPLE_REL(scanrel));

        /* Construct FROM clause */
        appendStringInfoString(buf, " FROM ");
        deparseFromExprForRel(buf, context->root, scanrel,
                              (bms_num_members(scanrel->relids) > 1),
                              (Index) 0, NULL, context->params_list);

        /* Construct WHERE clause */
        if (quals != NIL)
        {
                appendStringInfoString(buf, " WHERE ");
                appendConditions(quals, context);
        }
}

/*
 * Emit a target list that retrieves the columns specified in attrs_used.
 * This is used for both SELECT and RETURNING targetlists; the is_returning
 * parameter is true only for a RETURNING targetlist.
 *
 * The tlist text is appended to buf, and we also create an integer List
 * of the columns being retrieved, which is returned to *retrieved_attrs.
 *
 * If qualify_col is true, add relation alias before the column name.
 */
static void
deparseTargetList(StringInfo buf,
                  RangeTblEntry *rte,
                  Index rtindex,
                  Relation rel,
                  bool is_returning,
                  Bitmapset *attrs_used,
                  bool qualify_col,
                  List **retrieved_attrs)
{
        TupleDesc	tupdesc = RelationGetDescr(rel);
        bool		have_wholerow;
        bool		first;
        int			i;

        *retrieved_attrs = NIL;

        /* If there's a whole-row reference, we'll need all the columns. */
        have_wholerow = bms_is_member(0 - FirstLowInvalidHeapAttributeNumber,
                                      attrs_used);

        first = true;
        for (i = 1; i <= tupdesc->natts; i++)
        {
                Form_pg_attribute attr = TupleDescAttr(tupdesc, i - 1);

                /* Ignore dropped attributes. */
                if (attr->attisdropped)
                {
                        continue;
                }

                if (have_wholerow ||
                                bms_is_member(i - FirstLowInvalidHeapAttributeNumber,
                                              attrs_used))
                {
                        if (!first)
                        {
                                appendStringInfoString(buf, ", ");
                        }
                        else if (is_returning)
                        {
                                appendStringInfoString(buf, " RETURNING ");
                        }
                        first = false;

                        deparseColumnRef(buf, rtindex, i, rte, qualify_col);

                        *retrieved_attrs = lappend_int(*retrieved_attrs, i);
                }
        }

        /*
         * Add ctid and oid if needed.  We currently don't support retrieving any
         * other system columns.
         */
        if (bms_is_member(SelfItemPointerAttributeNumber -
                          FirstLowInvalidHeapAttributeNumber,
                          attrs_used))
        {
                if (!first)
                {
                        appendStringInfoString(buf, ", ");
                }
                else if (is_returning)
                {
                        appendStringInfoString(buf, " RETURNING ");
                }
                first = false;

                if (qualify_col)
                {
                        ADD_REL_QUALIFIER(buf, rtindex);
                }
                appendStringInfoString(buf, "ctid");

                *retrieved_attrs = lappend_int(*retrieved_attrs,
                                               SelfItemPointerAttributeNumber);
        }
        if (bms_is_member(ObjectIdAttributeNumber - FirstLowInvalidHeapAttributeNumber,
                          attrs_used))
        {
                if (!first)
                {
                        appendStringInfoString(buf, ", ");
                }
                else if (is_returning)
                {
                        appendStringInfoString(buf, " RETURNING ");
                }
                first = false;

                if (qualify_col)
                {
                        ADD_REL_QUALIFIER(buf, rtindex);
                }
                appendStringInfoString(buf, "oid");

                *retrieved_attrs = lappend_int(*retrieved_attrs,
                                               ObjectIdAttributeNumber);
        }

        /* Don't generate bad syntax if no undropped columns */
        if (first && !is_returning)
        {
                appendStringInfoString(buf, "NULL");
        }
}

/*
 * Deparse the appropriate locking clause (FOR UPDATE or FOR SHARE) for a
 * given relation (context->scanrel).
 */
static void
deparseLockingClause(deparse_expr_cxt *context)
{
        StringInfo	buf = context->buf;
        PlannerInfo *root = context->root;
        RelOptInfo *rel = context->scanrel;
        CHFdwRelationInfo *fpinfo = (CHFdwRelationInfo *) rel->fdw_private;
        int			relid = -1;

        while ((relid = bms_next_member(rel->relids, relid)) >= 0)
        {
                /*
                 * Ignore relation if it appears in a lower subquery.  Locking clause
                 * for such a relation is included in the subquery if necessary.
                 */
                if (bms_is_member(relid, fpinfo->lower_subquery_rels))
                {
                        continue;
                }

                /*
                 * Add FOR UPDATE/SHARE if appropriate.  We apply locking during the
                 * initial row fetch, rather than later on as is done for local
                 * tables. The extra roundtrips involved in trying to duplicate the
                 * local semantics exactly don't seem worthwhile (see also comments
                 * for RowMarkType).
                 *
                 * Note: because we actually run the query as a cursor, this assumes
                 * that DECLARE CURSOR ... FOR UPDATE is supported, which it isn't
                 * before 8.3.
                 */
                if (relid == root->parse->resultRelation &&
                                (root->parse->commandType == CMD_UPDATE ||
                                 root->parse->commandType == CMD_DELETE))
                {
                        /* Relation is UPDATE/DELETE target, so use FOR UPDATE */
                        appendStringInfoString(buf, " FOR UPDATE");

                        /* Add the relation alias if we are here for a join relation */
                        if (IS_JOIN_REL(rel))
                        {
                                appendStringInfo(buf, " OF %s%d", REL_ALIAS_PREFIX, relid);
                        }
                }
                else
                {
                        PlanRowMark *rc = get_plan_rowmark(root->rowMarks, relid);

                        if (rc)
                        {
                                /*
                                 * Relation is specified as a FOR UPDATE/SHARE target, so
                                 * handle that.  (But we could also see LCS_NONE, meaning this
                                 * isn't a target relation after all.)
                                 *
                                 * For now, just ignore any [NO] KEY specification, since (a)
                                 * it's not clear what that means for a remote table that we
                                 * don't have complete information about, and (b) it wouldn't
                                 * work anyway on older remote servers.  Likewise, we don't
                                 * worry about NOWAIT.
                                 */
                                switch (rc->strength)
                                {
                                        case LCS_NONE:
                                                /* No locking needed */
                                                break;
                                        case LCS_FORKEYSHARE:
                                        case LCS_FORSHARE:
                                                appendStringInfoString(buf, " FOR SHARE");
                                                break;
                                        case LCS_FORNOKEYUPDATE:
                                        case LCS_FORUPDATE:
                                                appendStringInfoString(buf, " FOR UPDATE");
                                                break;
                                }

                                /* Add the relation alias if we are here for a join relation */
                                if (bms_num_members(rel->relids) > 1 &&
                                                rc->strength != LCS_NONE)
                                {
                                        appendStringInfo(buf, " OF %s%d", REL_ALIAS_PREFIX, relid);
                                }
                        }
                }
        }
}

/*
 * Deparse conditions from the provided list and append them to buf.
 *
 * The conditions in the list are assumed to be ANDed. This function is used to
 * deparse WHERE clauses, JOIN .. ON clauses and HAVING clauses.
 *
 * Depending on the caller, the list elements might be either RestrictInfos
 * or bare clauses.
 */
static void
appendConditions(List *exprs, deparse_expr_cxt *context)
{
        int			nestlevel;
        ListCell   *lc;
        bool		is_first = true;
        StringInfo	buf = context->buf;

        /* Make sure any constants in the exprs are printed portably */
        nestlevel = set_transmission_modes();

        foreach (lc, exprs)
        {
                Expr	   *expr = (Expr *) lfirst(lc);

                /* Extract clause from RestrictInfo, if required */
                if (IsA(expr, RestrictInfo))
                {
                        expr = ((RestrictInfo *) expr)->clause;
                }

                /* Connect expressions with "AND" and parenthesize each condition. */
                if (!is_first)
                {
                        appendStringInfoString(buf, " AND ");
                }

                appendStringInfoChar(buf, '(');
                deparseExpr(expr, context);
                appendStringInfoChar(buf, ')');

                is_first = false;
        }

        reset_transmission_modes(nestlevel);
}

/* Output join name for given join type */
const char *
get_jointype_name(JoinType jointype)
{
        switch (jointype)
        {
                case JOIN_INNER:
                        return "INNER";

                case JOIN_LEFT:
                        return "LEFT";

                case JOIN_RIGHT:
                        return "RIGHT";

                case JOIN_FULL:
                        return "FULL";

                default:
                        /* Shouldn't come here, but protect from buggy code. */
                        elog(ERROR, "unsupported join type %d", jointype);
        }

        /* Keep compiler happy */
        return NULL;
}

/*
 * Deparse given targetlist and append it to context->buf.
 *
 * tlist is list of TargetEntry's which in turn contain Var nodes.
 *
 * retrieved_attrs is the list of continuously increasing integers starting
 * from 1. It has same number of entries as tlist.
 *
 * This is used for both SELECT and RETURNING targetlists; the is_returning
 * parameter is true only for a RETURNING targetlist.
 */
static void
deparseExplicitTargetList(List *tlist,
                          bool is_returning,
                          List **retrieved_attrs,
                          deparse_expr_cxt *context)
{
        ListCell   *lc;
        StringInfo	buf = context->buf;
        int			i = 0;

        elog(DEBUG2, "> %s:%d", __FUNCTION__, __LINE__);
        *retrieved_attrs = NIL;

        foreach (lc, tlist)
        {
                TargetEntry *tle = lfirst_node(TargetEntry, lc);

                if (i > 0)
                {
                        appendStringInfoString(buf, ", ");
                }
                else if (is_returning)
                {
                        appendStringInfoString(buf, " RETURNING ");
                }

                deparseExpr((Expr *) tle->expr, context);

                *retrieved_attrs = lappend_int(*retrieved_attrs, i + 1);
                i++;
        }

        if (i == 0 && !is_returning)
        {
                appendStringInfoString(buf, "NULL");
        }
        elog(DEBUG2, "< %s:%d", __FUNCTION__, __LINE__);
}

/*
 * Emit expressions specified in the given relation's reltarget.
 *
 * This is used for deparsing the given relation as a subquery.
 */
static void
deparseSubqueryTargetList(deparse_expr_cxt *context)
{
        StringInfo	buf = context->buf;
        RelOptInfo *foreignrel = context->foreignrel;
        bool		first;
        ListCell   *lc;

        /* Should only be called in these cases. */
        Assert(IS_SIMPLE_REL(foreignrel) || IS_JOIN_REL(foreignrel));

        first = true;
        foreach (lc, foreignrel->reltarget->exprs)
        {
                Node	   *node = (Node *) lfirst(lc);

                if (!first)
                {
                        appendStringInfoString(buf, ", ");
                }
                first = false;

                deparseExpr((Expr *) node, context);
        }

        /* Don't generate bad syntax if no expressions */
        if (first)
        {
                appendStringInfoString(buf, "NULL");
        }
}

/*
 * Construct FROM clause for given relation
 *
 * The function constructs ... JOIN ... ON ... for join relation. For a base
 * relation it just returns schema-qualified tablename, with the appropriate
 * alias if so requested.
 *
 * 'ignore_rel' is either zero or the RT index of a target relation.  In the
 * latter case the function constructs FROM clause of UPDATE or USING clause
 * of DELETE; it deparses the join relation as if the relation never contained
 * the target relation, and creates a List of conditions to be deparsed into
 * the top-level WHERE clause, which is returned to *ignore_conds.
 */
static void
deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
                      bool use_alias, Index ignore_rel, List **ignore_conds,
                      List **params_list)
{
        CHFdwRelationInfo *fpinfo = (CHFdwRelationInfo *) foreignrel->fdw_private;

        if (IS_JOIN_REL(foreignrel))
        {
                StringInfoData join_sql_o;
                StringInfoData join_sql_i;
                RelOptInfo *outerrel = fpinfo->outerrel;
                RelOptInfo *innerrel = fpinfo->innerrel;
                bool		outerrel_is_target = false;
                bool		innerrel_is_target = false;

                if (ignore_rel > 0 && bms_is_member(ignore_rel, foreignrel->relids))
                {
                        /*
                         * If this is an inner join, add joinclauses to *ignore_conds and
                         * set it to empty so that those can be deparsed into the WHERE
                         * clause.  Note that since the target relation can never be
                         * within the nullable side of an outer join, those could safely
                         * be pulled up into the WHERE clause (see foreign_join_ok()).
                         * Note also that since the target relation is only inner-joined
                         * to any other relation in the query, all conditions in the join
                         * tree mentioning the target relation could be deparsed into the
                         * WHERE clause by doing this recursively.
                         */
                        if (fpinfo->jointype == JOIN_INNER)
                        {
                                *ignore_conds = list_concat(*ignore_conds,
                                                            list_copy(fpinfo->joinclauses));
                                fpinfo->joinclauses = NIL;
                        }

                        /*
                         * Check if either of the input relations is the target relation.
                         */
                        if (outerrel->relid == ignore_rel)
                        {
                                outerrel_is_target = true;
                        }
                        else if (innerrel->relid == ignore_rel)
                        {
                                innerrel_is_target = true;
                        }
                }

                /* Deparse outer relation if not the target relation. */
                if (!outerrel_is_target)
                {
                        initStringInfo(&join_sql_o);
                        deparseRangeTblRef(&join_sql_o, root, outerrel,
                                           fpinfo->make_outerrel_subquery,
                                           ignore_rel, ignore_conds, params_list);

                        /*
                         * If inner relation is the target relation, skip deparsing it.
                         * Note that since the join of the target relation with any other
                         * relation in the query is an inner join and can never be within
                         * the nullable side of an outer join, the join could be
                         * interchanged with higher-level joins (cf. identity 1 on outer
                         * join reordering shown in src/backend/optimizer/README), which
                         * means it's safe to skip the target-relation deparsing here.
                         */
                        if (innerrel_is_target)
                        {
                                Assert(fpinfo->jointype == JOIN_INNER);
                                Assert(fpinfo->joinclauses == NIL);
                                appendStringInfo(buf, "%s", join_sql_o.data);
                                return;
                        }
                }

                /* Deparse inner relation if not the target relation. */
                if (!innerrel_is_target)
                {
                        initStringInfo(&join_sql_i);
                        deparseRangeTblRef(&join_sql_i, root, innerrel,
                                           fpinfo->make_innerrel_subquery,
                                           ignore_rel, ignore_conds, params_list);

                        /*
                         * If outer relation is the target relation, skip deparsing it.
                         * See the above note about safety.
                         */
                        if (outerrel_is_target)
                        {
                                Assert(fpinfo->jointype == JOIN_INNER);
                                Assert(fpinfo->joinclauses == NIL);
                                appendStringInfo(buf, "%s", join_sql_i.data);
                                return;
                        }
                }

                /* Neither of the relations is the target relation. */
                Assert(!outerrel_is_target && !innerrel_is_target);

                /*
                 * For a join relation FROM clause entry is deparsed as
                 *
                 * ((outer relation) <join type> (inner relation) ON (joinclauses))
                 */
                appendStringInfo(buf, " %s ALL %s JOIN %s ON ", join_sql_o.data,
                                 get_jointype_name(fpinfo->jointype), join_sql_i.data);

                /* Append join clause; (TRUE) if no join clause */
                if (fpinfo->joinclauses)
                {
                        deparse_expr_cxt context;

                        context.buf = buf;
                        context.foreignrel = foreignrel;
                        context.scanrel = foreignrel;
                        context.root = root;
                        context.params_list = params_list;

                        appendStringInfoChar(buf, '(');
                        appendConditions(fpinfo->joinclauses, &context);
                        appendStringInfoChar(buf, ')');
                }
                else
                {
                        appendStringInfoString(buf, "(TRUE)");
                }

        }
        else
        {
                RangeTblEntry *rte = planner_rt_fetch(foreignrel->relid, root);

                /*
                 * Core code already has some lock on each rel being planned, so we
                 * can use NoLock here.
                 */
                Relation	rel = heap_open(rte->relid, NoLock);

                deparseRelation(buf, rel);

                /*
                 * Add a unique alias to avoid any conflict in relation names due to
                 * pulled up subqueries in the query being built for a pushed down
                 * join.
                 */
                if (use_alias)
                {
                        appendStringInfo(buf, " %s%d", REL_ALIAS_PREFIX, foreignrel->relid);
                }

                heap_close(rel, NoLock);
        }
}

/*
 * Append FROM clause entry for the given relation into buf.
 */
static void
deparseRangeTblRef(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
                   bool make_subquery, Index ignore_rel, List **ignore_conds,
                   List **params_list)
{
        CHFdwRelationInfo *fpinfo = (CHFdwRelationInfo *) foreignrel->fdw_private;

        /* Should only be called in these cases. */
        Assert(IS_SIMPLE_REL(foreignrel) || IS_JOIN_REL(foreignrel));

        Assert(fpinfo->local_conds == NIL);

        /* If make_subquery is true, deparse the relation as a subquery. */
        if (make_subquery)
        {
                List	   *retrieved_attrs;
                int			ncols;

                /*
                 * The given relation shouldn't contain the target relation, because
                 * this should only happen for input relations for a full join, and
                 * such relations can never contain an UPDATE/DELETE target.
                 */
                Assert(ignore_rel == 0 ||
                       !bms_is_member(ignore_rel, foreignrel->relids));

                /* Deparse the subquery representing the relation. */
                appendStringInfoChar(buf, '(');
                deparseSelectStmtForRel(buf, root, foreignrel, NIL,
                                        fpinfo->remote_conds, NIL, true,
                                        &retrieved_attrs, params_list);
                appendStringInfoChar(buf, ')');

                /* Append the relation alias. */
                appendStringInfo(buf, " %s%d", SUBQUERY_REL_ALIAS_PREFIX,
                                 fpinfo->relation_index);

                /*
                 * Append the column aliases if needed.  Note that the subquery emits
                 * expressions specified in the relation's reltarget (see
                 * deparseSubqueryTargetList).
                 */
                ncols = list_length(foreignrel->reltarget->exprs);
                if (ncols > 0)
                {
                        int			i;

                        appendStringInfoChar(buf, '(');
                        for (i = 1; i <= ncols; i++)
                        {
                                if (i > 1)
                                {
                                        appendStringInfoString(buf, ", ");
                                }

                                appendStringInfo(buf, "%s%d", SUBQUERY_COL_ALIAS_PREFIX, i);
                        }
                        appendStringInfoChar(buf, ')');
                }
        }
        else
                deparseFromExprForRel(buf, root, foreignrel, true, ignore_rel,
                                      ignore_conds, params_list);
}

/*
 * deparse remote INSERT statement
 *
 * The statement text is appended to buf, and we also create an integer List
 * of the columns being retrieved by RETURNING (if any), which is returned
 * to *retrieved_attrs.
 */
void
deparseInsertSql(StringInfo buf, RangeTblEntry *rte,
                 Index rtindex, Relation rel,
                 List *targetAttrs, bool doNothing,
                 List *returningList, List **retrieved_attrs)
{
        bool    first;
        ListCell   *lc;

        appendStringInfoString(buf, "INSERT INTO ");
        deparseRelation(buf, rel);

        if (targetAttrs)
        {
                appendStringInfoChar(buf, '(');

                first = true;
                foreach (lc, targetAttrs)
                {
                        int			attnum = lfirst_int(lc);

                        if (!first)
                        {
                                appendStringInfoString(buf, ", ");
                        }
                        first = false;

                        deparseColumnRef(buf, rtindex, attnum, rte, false);
                }
                appendStringInfoChar(buf, ')');
        }
}


/*
 * Construct SELECT statement to acquire size in blocks of given relation.
 *
 * Note: we use local definition of block size, not remote definition.
 * This is perhaps debatable.
 *
 * Note: pg_relation_size() exists in 8.1 and later.
 */
void
deparseAnalyzeSizeSql(StringInfo buf, Relation rel)
{
        StringInfoData relname;

        /* We'll need the remote relation name as a literal. */
        initStringInfo(&relname);
        deparseRelation(&relname, rel);
}

/*
 * Construct SELECT statement to acquire sample rows of given relation.
 *
 * SELECT command is appended to buf, and list of columns retrieved
 * is returned to *retrieved_attrs.
 */
void
deparseAnalyzeSql(StringInfo buf, Relation rel, List **retrieved_attrs)
{
        Oid			relid = RelationGetRelid(rel);
        TupleDesc	tupdesc = RelationGetDescr(rel);
        int			i;
        char	   *colname;
        List	   *options;
        ListCell   *lc;
        bool		first = true;

        *retrieved_attrs = NIL;

        appendStringInfoString(buf, "SELECT ");
        for (i = 0; i < tupdesc->natts; i++)
        {
                /* Ignore dropped columns. */
                if (TupleDescAttr(tupdesc, i)->attisdropped)
                {
                        continue;
                }

                if (!first)
                {
                        appendStringInfoString(buf, ", ");
                }
                first = false;

                /* Use attribute name or column_name option. */
                colname = NameStr(TupleDescAttr(tupdesc, i)->attname);
                options = GetForeignColumnOptions(relid, i + 1);

                foreach (lc, options)
                {
                        DefElem    *def = (DefElem *) lfirst(lc);

                        if (strcmp(def->defname, "column_name") == 0)
                        {
                                colname = defGetString(def);
                                break;
                        }
                }

                appendStringInfoString(buf, quote_identifier(colname));

                *retrieved_attrs = lappend_int(*retrieved_attrs, i + 1);
        }

        /* Don't generate bad syntax for zero-column relation. */
        if (first)
        {
                appendStringInfoString(buf, "NULL");
        }

        /*
         * Construct FROM clause
         */
        appendStringInfoString(buf, " FROM ");
        deparseRelation(buf, rel);
}

/*
 * Construct name to use for given column, and emit it into buf.
 * If it has a column_name FDW option, use that instead of attribute name.
 *
 * If qualify_col is true, qualify column name with the alias of relation.
 */
static void
deparseColumnRef(StringInfo buf, int varno, int varattno, RangeTblEntry *rte,
                 bool qualify_col)
{
        /* We support fetching the remote side's CTID and OID. */
        if (varattno == SelfItemPointerAttributeNumber)
        {
                if (qualify_col)
                {
                        ADD_REL_QUALIFIER(buf, varno);
                }
                appendStringInfoString(buf, "ctid");
        }
        else if (varattno == ObjectIdAttributeNumber)
        {
                if (qualify_col)
                {
                        ADD_REL_QUALIFIER(buf, varno);
                }
                appendStringInfoString(buf, "oid");
        }
        else if (varattno < 0)
        {
                /*
                 * All other system attributes are fetched as 0, except for table OID,
                 * which is fetched as the local table OID.  However, we must be
                 * careful; the table could be beneath an outer join, in which case it
                 * must go to NULL whenever the rest of the row does.
                 */
                Oid			fetchval = 0;

                if (varattno == TableOidAttributeNumber)
                {
                        fetchval = rte->relid;
                }

                if (qualify_col)
                {
                        appendStringInfoString(buf, "CASE WHEN (");
                        ADD_REL_QUALIFIER(buf, varno);
                        appendStringInfo(buf, "*) IS NOT NULL THEN %u END", fetchval);
                }
                else
                {
                        appendStringInfo(buf, "%u", fetchval);
                }
        }
        else if (varattno == 0)
        {
                /* Whole row reference */
                Relation	rel;
                Bitmapset  *attrs_used;

                /* Required only to be passed down to deparseTargetList(). */
                List	   *retrieved_attrs;

                /*
                 * The lock on the relation will be held by upper callers, so it's
                 * fine to open it with no lock here.
                 */
                rel = heap_open(rte->relid, NoLock);

                /*
                 * The local name of the foreign table can not be recognized by the
                 * foreign server and the table it references on foreign server might
                 * have different column ordering or different columns than those
                 * declared locally. Hence we have to deparse whole-row reference as
                 * ROW(columns referenced locally). Construct this by deparsing a
                 * "whole row" attribute.
                 */
                attrs_used = bms_add_member(NULL,
                                            0 - FirstLowInvalidHeapAttributeNumber);

                /*
                 * In case the whole-row reference is under an outer join then it has
                 * to go NULL whenever the rest of the row goes NULL. Deparsing a join
                 * query would always involve multiple relations, thus qualify_col
                 * would be true.
                 */
                if (qualify_col)
                {
                        appendStringInfoString(buf, "CASE WHEN (");
                        ADD_REL_QUALIFIER(buf, varno);
                        appendStringInfoString(buf, "*) IS NOT NULL THEN ");
                }

                appendStringInfoString(buf, "ROW(");
                deparseTargetList(buf, rte, varno, rel, false, attrs_used, qualify_col,
                                  &retrieved_attrs);
                appendStringInfoChar(buf, ')');

                /* Complete the CASE WHEN statement started above. */
                if (qualify_col)
                {
                        appendStringInfoString(buf, " END");
                }

                heap_close(rel, NoLock);
                bms_free(attrs_used);
        }
        else
        {
                char	   *colname = NULL;
                List	   *options;
                ListCell   *lc;

                /* varno must not be any of OUTER_VAR, INNER_VAR and INDEX_VAR. */
                Assert(!IS_SPECIAL_VARNO(varno));

                /*
                 * If it's a column of a foreign table, and it has the column_name FDW
                 * option, use that value.
                 */
                options = GetForeignColumnOptions(rte->relid, varattno);
                foreach (lc, options)
                {
                        DefElem    *def = (DefElem *) lfirst(lc);

                        if (strcmp(def->defname, "column_name") == 0)
                        {
                                colname = defGetString(def);
                                break;
                        }
                }

                /*
                 * If it's a column of a regular table or it doesn't have column_name
                 * FDW option, use attribute name.
                 */
                if (colname == NULL)
                {
                        colname = get_attname(rte->relid, varattno, false);
                }

                if (qualify_col)
                {
                        ADD_REL_QUALIFIER(buf, varno);
                }

                appendStringInfoString(buf, quote_identifier(colname));
        }
}

/*
 * Append remote name of specified foreign table to buf.
 * Use value of table_name FDW option (if any) instead of relation's name.
 * Similarly, schema_name FDW option overrides schema name.
 */
static void
deparseRelation(StringInfo buf, Relation rel)
{
        ForeignTable *table;
        const char *relname = NULL;
        char       *driver;
        char       *host;
        int        port;
        char       *username;
        char       *password;
        char       *dbname;
        ForeignServer *server = get_foreign_server(rel);
        ListCell    *lc;

        ExtractConnectionOptions(server->options, &driver, &host, &port, &dbname,
                                 &username, &password);

        /* obtain additional catalog information. */
        table = GetForeignTable(RelationGetRelid(rel));

        /*
         * Use value of FDW options if any, instead of the name of object itself.
         */
        foreach (lc, table->options)
        {
                DefElem    *def = (DefElem *) lfirst(lc);

                if (strcmp(def->defname, "table_name") == 0)
                {
                        relname = defGetString(def);
                }
        }
        if (relname == NULL)
        {
                relname = RelationGetRelationName(rel);
        }

        appendStringInfo(buf, "%s.%s", quote_identifier(dbname),
                         quote_identifier(relname));
}

/*
 * Append a SQL string literal representing "val" to buf.
 */
void
deparseStringLiteral(StringInfo buf, const char *val)
{
        const char *valptr;

        /*
         * Rather than making assumptions about the remote server's value of
         * standard_conforming_strings, always use E'foo' syntax if there are any
         * backslashes.  This will fail on remote servers before 8.1, but those
         * are long out of support.
         */
        if (strchr(val, '\\') != NULL)
        {
                appendStringInfoChar(buf, ESCAPE_STRING_SYNTAX);
        }
        appendStringInfoChar(buf, '\'');
        for (valptr = val; *valptr; valptr++)
        {
                char		ch = *valptr;

                if (SQL_STR_DOUBLE(ch, true))
                {
                        appendStringInfoChar(buf, ch);
                }
                appendStringInfoChar(buf, ch);
        }
        appendStringInfoChar(buf, '\'');
}

/*
 * Deparse given expression into context->buf.
 *
 * This function must support all the same node types that foreign_expr_walker
 * accepts.
 *
 * Note: unlike ruleutils.c, we just use a simple hard-wired parenthesization
 * scheme: anything more complex than a Var, Const, function call or cast
 * should be self-parenthesized.
 */
static void
deparseExpr(Expr *node, deparse_expr_cxt *context)
{
        if (node == NULL)
        {
                return;
        }

        switch (nodeTag(node))
        {
                case T_Var:
                        deparseVar((Var *) node, context);
                        break;
                case T_Const:
                        deparseConst((Const *) node, context, 0);
                        break;
                case T_Param:
                        deparseParam((Param *) node, context);
                        break;
                case T_ArrayRef:
                        deparseArrayRef((ArrayRef *) node, context);
                        break;
                case T_FuncExpr:
                        deparseFuncExpr((FuncExpr *) node, context);
                        break;
                case T_OpExpr:
                        deparseOpExpr((OpExpr *) node, context);
                        break;
                case T_DistinctExpr:
                        deparseDistinctExpr((DistinctExpr *) node, context);
                        break;
                case T_ScalarArrayOpExpr:
                        deparseScalarArrayOpExpr((ScalarArrayOpExpr *) node, context);
                        break;
                case T_RelabelType:
                        deparseRelabelType((RelabelType *) node, context);
                        break;
                case T_BoolExpr:
                        deparseBoolExpr((BoolExpr *) node, context);
                        break;
                case T_NullTest:
                        deparseNullTest((NullTest *) node, context);
                        break;
                case T_ArrayExpr:
                        deparseArrayExpr((ArrayExpr *) node, context);
                        break;
                case T_Aggref:
                        deparseAggref((Aggref *) node, context);
                        break;
                default:
                        elog(ERROR, "unsupported expression type for deparse: %d",
                             (int) nodeTag(node));
                        break;
        }
}

/*
 * Deparse given Var node into context->buf.
 *
 * If the Var belongs to the foreign relation, just print its remote name.
 * Otherwise, it's effectively a Param (and will in fact be a Param at
 * run time).  Handle it the same way we handle plain Params --- see
 * deparseParam for comments.
 */
static void
deparseVar(Var *node, deparse_expr_cxt *context)
{
        Relids		relids = context->scanrel->relids;
        int			relno;
        int			colno;

        /* Qualify columns when multiple relations are involved. */
        bool		qualify_col = (bms_num_members(relids) > 1);

        /*
         * If the Var belongs to the foreign relation that is deparsed as a
         * subquery, use the relation and column alias to the Var provided by the
         * subquery, instead of the remote name.
         */
        if (is_subquery_var(node, context->scanrel, &relno, &colno))
        {
                appendStringInfo(context->buf, "%s%d.%s%d",
                                 SUBQUERY_REL_ALIAS_PREFIX, relno,
                                 SUBQUERY_COL_ALIAS_PREFIX, colno);
                return;
        }

        if (bms_is_member(node->varno, relids) && node->varlevelsup == 0)
                deparseColumnRef(context->buf, node->varno, node->varattno,
                                 planner_rt_fetch(node->varno, context->root),
                                 qualify_col);
        else
        {
                /* Treat like a Param */
                if (context->params_list)
                {
                        int			pindex = 0;
                        ListCell   *lc;

                        /* find its index in params_list */
                        foreach (lc, *context->params_list)
                        {
                                pindex++;
                                if (equal(node, (Node *) lfirst(lc)))
                                {
                                        break;
                                }
                        }
                        if (lc == NULL)
                        {
                                /* not in list, so add it */
                                pindex++;
                                *context->params_list = lappend(*context->params_list, node);
                        }

                        printRemoteParam(pindex, node->vartype, node->vartypmod, context);
                }
                else
                {
                        printRemotePlaceholder(node->vartype, node->vartypmod, context);
                }
        }
}

/*
 * Deparse given constant value into context->buf.
 *
 * This function has to be kept in sync with ruleutils.c's get_const_expr.
 * As for that function, showtype can be -1 to never show "::typename" decoration,
 * or +1 to always show it, or 0 to show it only if the constant wouldn't be assumed
 * to be the right type by default.
 */
static void
deparseConst(Const *node, deparse_expr_cxt *context, int showtype)
{
        StringInfo	buf = context->buf;
        Oid			typoutput;
        bool		typIsVarlena;
        char	   *extval;

        if (node->constisnull)
        {
                appendStringInfoString(buf, "NULL");
                return;
        }

        getTypeOutputInfo(node->consttype,
                          &typoutput, &typIsVarlena);
        extval = OidOutputFunctionCall(typoutput, node->constvalue);

        switch (node->consttype)
        {
                case INT2OID:
                case INT4OID:
                case INT8OID:
                case OIDOID:
                case FLOAT4OID:
                case FLOAT8OID:
                case NUMERICOID:
                {
                        /*
                         * No need to quote unless it's a special value such as 'NaN'.
                         * See comments in get_const_expr().
                         */
                        if (strspn(extval, "0123456789+-eE.") == strlen(extval))
                        {
                                if (extval[0] == '+' || extval[0] == '-')
                                {
                                        appendStringInfo(buf, "(%s)", extval);
                                }
                                else
                                {
                                        appendStringInfoString(buf, extval);
                                }
                        }
                        else
                        {
                                appendStringInfo(buf, "'%s'", extval);
                        }
                }
                break;
                case BITOID:
                case VARBITOID:
                        appendStringInfo(buf, "B'%s'", extval);
                        break;
                case BOOLOID:
                        if (strcmp(extval, "t") == 0)
                        {
                                appendStringInfoString(buf, "true");
                        }
                        else
                        {
                                appendStringInfoString(buf, "false");
                        }
                        break;
                default:
                        deparseStringLiteral(buf, extval);
                        break;
        }
        pfree(extval);
}

/*
 * Deparse given Param node.
 *
 * If we're generating the query "for real", add the Param to
 * context->params_list if it's not already present, and then use its index
 * in that list as the remote parameter number.  During EXPLAIN, there's
 * no need to identify a parameter number.
 */
static void
deparseParam(Param *node, deparse_expr_cxt *context)
{
        if (context->params_list)
        {
                int			pindex = 0;
                ListCell   *lc;

                /* find its index in params_list */
                foreach (lc, *context->params_list)
                {
                        pindex++;
                        if (equal(node, (Node *) lfirst(lc)))
                        {
                                break;
                        }
                }
                if (lc == NULL)
                {
                        /* not in list, so add it */
                        pindex++;
                        *context->params_list = lappend(*context->params_list, node);
                }

                printRemoteParam(pindex, node->paramtype, node->paramtypmod, context);
        }
        else
        {
                printRemotePlaceholder(node->paramtype, node->paramtypmod, context);
        }
}

/*
 * Deparse an array subscript expression.
 */
static void
deparseArrayRef(ArrayRef *node, deparse_expr_cxt *context)
{
        StringInfo	buf = context->buf;
        ListCell   *lowlist_item;
        ListCell   *uplist_item;

        /* Always parenthesize the expression. */
        appendStringInfoChar(buf, '(');

        /*
         * Deparse referenced array expression first.  If that expression includes
         * a cast, we have to parenthesize to prevent the array subscript from
         * being taken as typename decoration.  We can avoid that in the typical
         * case of subscripting a Var, but otherwise do it.
         */
        if (IsA(node->refexpr, Var))
        {
                deparseExpr(node->refexpr, context);
        }
        else
        {
                appendStringInfoChar(buf, '(');
                deparseExpr(node->refexpr, context);
                appendStringInfoChar(buf, ')');
        }

        /* Deparse subscript expressions. */
        lowlist_item = list_head(node->reflowerindexpr);	/* could be NULL */
        foreach (uplist_item, node->refupperindexpr)
        {
                appendStringInfoChar(buf, '[');
                if (lowlist_item)
                {
                        deparseExpr(lfirst(lowlist_item), context);
                        appendStringInfoChar(buf, ':');
                        lowlist_item = lnext(lowlist_item);
                }
                deparseExpr(lfirst(uplist_item), context);
                appendStringInfoChar(buf, ']');
        }

        appendStringInfoChar(buf, ')');
}

/*
 * Deparse a function call.
 */
static void
deparseFuncExpr(FuncExpr *node, deparse_expr_cxt *context)
{
        StringInfo	buf = context->buf;
        bool		use_variadic;
        bool		first;
        ListCell   *arg;

        /*
         * If the function call came from an implicit coercion, then just show the
         * first argument.
         */
        if (node->funcformat == COERCE_IMPLICIT_CAST)
        {
                deparseExpr((Expr *) linitial(node->args), context);
                return;
        }

        /*
         * If the function call came from a cast, then show the first argument
         * plus an explicit cast operation.
         */
        if (node->funcformat == COERCE_EXPLICIT_CAST)
        {
                int32		coercedTypmod;

                /* Get the typmod if this is a length-coercion function */
                (void) exprIsLengthCoercion((Node *) node, &coercedTypmod);

                deparseExpr((Expr *) linitial(node->args), context);
                return;
        }

        /* Check if need to print VARIADIC (cf. ruleutils.c) */
        use_variadic = node->funcvariadic;

        /*
         * Normal function: display as proname(args).
         */
        appendFunctionName(node->funcid, context);
        appendStringInfoChar(buf, '(');

        /* ... and all the arguments */
        first = true;
        foreach (arg, node->args)
        {
                if (!first)
                {
                        appendStringInfoString(buf, ", ");
                }
                if (use_variadic && lnext(arg) == NULL)
                {
                        appendStringInfoString(buf, "VARIADIC ");
                }
                deparseExpr((Expr *) lfirst(arg), context);
                first = false;
        }
        appendStringInfoChar(buf, ')');
}

/*
 * Deparse given operator expression.   To avoid problems around
 * priority of operations, we always parenthesize the arguments.
 */
static void
deparseOpExpr(OpExpr *node, deparse_expr_cxt *context)
{
        StringInfo	buf = context->buf;
        HeapTuple	tuple;
        Form_pg_operator form;
        char		oprkind;
        ListCell   *arg;

        /* Retrieve information about the operator from system catalog. */
        tuple = SearchSysCache1(OPEROID, ObjectIdGetDatum(node->opno));
        if (!HeapTupleIsValid(tuple))
        {
                elog(ERROR, "cache lookup failed for operator %u", node->opno);
        }
        form = (Form_pg_operator) GETSTRUCT(tuple);
        oprkind = form->oprkind;

        /* Sanity check. */
        Assert((oprkind == 'r' && list_length(node->args) == 1) ||
               (oprkind == 'l' && list_length(node->args) == 1) ||
               (oprkind == 'b' && list_length(node->args) == 2));

        /* Always parenthesize the expression. */
        appendStringInfoChar(buf, '(');

        /* Deparse left operand. */
        if (oprkind == 'r' || oprkind == 'b')
        {
                arg = list_head(node->args);
                deparseExpr(lfirst(arg), context);
                appendStringInfoChar(buf, ' ');
        }

        /* Deparse operator name. */
        deparseOperatorName(buf, form);

        /* Deparse right operand. */
        if (oprkind == 'l' || oprkind == 'b')
        {
                arg = list_tail(node->args);
                appendStringInfoChar(buf, ' ');
                deparseExpr(lfirst(arg), context);
        }

        appendStringInfoChar(buf, ')');

        ReleaseSysCache(tuple);
}

/*
 * Print the name of an operator.
 */
static void
deparseOperatorName(StringInfo buf, Form_pg_operator opform)
{
        char	   *opname;

        /* opname is not a SQL identifier, so we should not quote it. */
        opname = NameStr(opform->oprname);

        /* Print schema name only if it's not pg_catalog */
        if (opform->oprnamespace != PG_CATALOG_NAMESPACE)
        {
                const char *opnspname;

                opnspname = get_namespace_name(opform->oprnamespace);
                /* Print fully qualified operator name. */
                appendStringInfo(buf, "OPERATOR(%s.%s)",
                                 quote_identifier(opnspname), opname);
        }
	    else
	    {
		    if (strcmp(opname, "~~") == 0)
		    {
			    appendStringInfoString(buf, "LIKE");
		    }
		    else if (strcmp(opname, "~~*") == 0)
		    {
                appendStringInfoString(buf, "LIKE");
            }
		    else if (strcmp(opname, "!~~") == 0)
		    {
			    appendStringInfoString(buf, "NOT LIKE");
		    }
		    else if (strcmp(opname, "!~~*") == 0)
		    {
                appendStringInfoString(buf, "NOT LIKE");
            }
		    else
		    {
			    appendStringInfoString(buf, opname);
		    }
    }
 }

/*
 * Deparse IS DISTINCT FROM.
 */
static void
deparseDistinctExpr(DistinctExpr *node, deparse_expr_cxt *context)
{
        StringInfo	buf = context->buf;

        Assert(list_length(node->args) == 2);

        appendStringInfoChar(buf, '(');
        deparseExpr(linitial(node->args), context);
        appendStringInfoString(buf, " IS DISTINCT FROM ");
        deparseExpr(lsecond(node->args), context);
        appendStringInfoChar(buf, ')');
}

/*
 * Deparse given ScalarArrayOpExpr expression.  To avoid problems
 * around priority of operations, we always parenthesize the arguments.
 */
static void
deparseScalarArrayOpExpr(ScalarArrayOpExpr *node, deparse_expr_cxt *context)
{
        StringInfo	buf = context->buf;
        HeapTuple	tuple;
        Form_pg_operator form;
        Expr	   *arg1;
        Expr	   *arg2;

        /* Retrieve information about the operator from system catalog. */
        tuple = SearchSysCache1(OPEROID, ObjectIdGetDatum(node->opno));
        if (!HeapTupleIsValid(tuple))
        {
                elog(ERROR, "cache lookup failed for operator %u", node->opno);
        }
        form = (Form_pg_operator) GETSTRUCT(tuple);

        /* Sanity check. */
        Assert(list_length(node->args) == 2);

        /* Always parenthesize the expression. */
        appendStringInfoChar(buf, '(');

        /* Deparse left operand. */
        arg1 = linitial(node->args);
        deparseExpr(arg1, context);
        appendStringInfoChar(buf, ' ');

        /* Deparse operator name plus decoration. */
        deparseOperatorName(buf, form);
        appendStringInfo(buf, " %s (", node->useOr ? "ANY" : "ALL");

        /* Deparse right operand. */
        arg2 = lsecond(node->args);
        deparseExpr(arg2, context);

        appendStringInfoChar(buf, ')');

        /* Always parenthesize the expression. */
        appendStringInfoChar(buf, ')');

        ReleaseSysCache(tuple);
}

/*
 * Deparse a RelabelType (binary-compatible cast) node.
 */
static void
deparseRelabelType(RelabelType *node, deparse_expr_cxt *context)
{
        deparseExpr(node->arg, context);
}

/*
 * Deparse a BoolExpr node.
 */
static void
deparseBoolExpr(BoolExpr *node, deparse_expr_cxt *context)
{
        StringInfo	buf = context->buf;
        const char *op = NULL;		/* keep compiler quiet */
        bool		first;
        ListCell   *lc;

        switch (node->boolop)
        {
                case AND_EXPR:
                        op = "AND";
                        break;
                case OR_EXPR:
                        op = "OR";
                        break;
                case NOT_EXPR:
                        appendStringInfoString(buf, "(NOT ");
                        deparseExpr(linitial(node->args), context);
                        appendStringInfoChar(buf, ')');
                        return;
        }

        appendStringInfoChar(buf, '(');
        first = true;
        foreach (lc, node->args)
        {
                if (!first)
                {
                        appendStringInfo(buf, " %s ", op);
                }
                deparseExpr((Expr *) lfirst(lc), context);
                first = false;
        }
        appendStringInfoChar(buf, ')');
}

/*
 * Deparse IS [NOT] NULL expression.
 */
static void
deparseNullTest(NullTest *node, deparse_expr_cxt *context)
{
        StringInfo	buf = context->buf;

        appendStringInfoChar(buf, '(');
        deparseExpr(node->arg, context);

        /*
         * For scalar inputs, we prefer to print as IS [NOT] NULL, which is
         * shorter and traditional.  If it's a rowtype input but we're applying a
         * scalar test, must print IS [NOT] DISTINCT FROM NULL to be semantically
         * correct.
         */
        if (node->argisrow || !type_is_rowtype(exprType((Node *) node->arg)))
        {
                if (node->nulltesttype == IS_NULL)
                {
                        appendStringInfoString(buf, " IS NULL)");
                }
                else
                {
                        appendStringInfoString(buf, " IS NOT NULL)");
                }
        }
        else
        {
                if (node->nulltesttype == IS_NULL)
                {
                        appendStringInfoString(buf, " IS NOT DISTINCT FROM NULL)");
                }
                else
                {
                        appendStringInfoString(buf, " IS DISTINCT FROM NULL)");
                }
        }
}

/*
 * Deparse ARRAY[...] construct.
 */
static void
deparseArrayExpr(ArrayExpr *node, deparse_expr_cxt *context)
{
}

/*
 * Deparse an Aggref node.
 */
static void
deparseAggref(Aggref *node, deparse_expr_cxt *context)
{
        StringInfo	buf = context->buf;
        bool		use_variadic;

        /* Only basic, non-split aggregation accepted. */
        Assert(node->aggsplit == AGGSPLIT_SIMPLE);

        /* Check if need to print VARIADIC (cf. ruleutils.c) */
        use_variadic = node->aggvariadic;

        /* Find aggregate name from aggfnoid which is a pg_proc entry */
        appendFunctionName(node->aggfnoid, context);
        appendStringInfoChar(buf, '(');

        /* Add DISTINCT */
        appendStringInfoString(buf, (node->aggdistinct != NIL) ? "DISTINCT " : "");

        if (AGGKIND_IS_ORDERED_SET(node->aggkind))
        {
                /* Add WITHIN GROUP (ORDER BY ..) */
                ListCell   *arg;
                bool		first = true;

                Assert(!node->aggvariadic);
                Assert(node->aggorder != NIL);

                foreach (arg, node->aggdirectargs)
                {
                        if (!first)
                        {
                                appendStringInfoString(buf, ", ");
                        }
                        first = false;

                        deparseExpr((Expr *) lfirst(arg), context);
                }

                appendStringInfoString(buf, ") WITHIN GROUP (ORDER BY ");
                appendAggOrderBy(node->aggorder, node->args, context);
        }
        else
        {
                /* aggstar can be set only in zero-argument aggregates */
                if (node->aggstar)
                {
                        appendStringInfoChar(buf, '*');
                }
                else
                {
                        ListCell   *arg;
                        bool		first = true;

                        /* Add all the arguments */
                        foreach (arg, node->args)
                        {
                                TargetEntry *tle = (TargetEntry *) lfirst(arg);
                                Node	   *n = (Node *) tle->expr;

                                if (tle->resjunk)
                                {
                                        continue;
                                }

                                if (!first)
                                {
                                        appendStringInfoString(buf, ", ");
                                }
                                first = false;

                                /* Add VARIADIC */
                                if (use_variadic && lnext(arg) == NULL)
                                {
                                        appendStringInfoString(buf, "VARIADIC ");
                                }

                                deparseExpr((Expr *) n, context);
                        }
                }

                /* Add ORDER BY */
                if (node->aggorder != NIL)
                {
                        appendStringInfoString(buf, " ORDER BY ");
                        appendAggOrderBy(node->aggorder, node->args, context);
                }
        }

        /* Add FILTER (WHERE ..) */
        if (node->aggfilter != NULL)
        {
                appendStringInfoString(buf, ") FILTER (WHERE ");
                deparseExpr((Expr *) node->aggfilter, context);
        }

        appendStringInfoChar(buf, ')');
}

/*
 * Append ORDER BY within aggregate function.
 */
static void
appendAggOrderBy(List *orderList, List *targetList, deparse_expr_cxt *context)
{
        StringInfo	buf = context->buf;
        ListCell   *lc;
        bool		first = true;

        foreach (lc, orderList)
        {
                SortGroupClause *srt = (SortGroupClause *) lfirst(lc);
                Node	   *sortexpr;
                Oid			sortcoltype;
                TypeCacheEntry *typentry;

                if (!first)
                {
                        appendStringInfoString(buf, ", ");
                }
                first = false;

                sortexpr = deparseSortGroupClause(srt->tleSortGroupRef, targetList,
                                                  false, context);
                sortcoltype = exprType(sortexpr);
                /* See whether operator is default < or > for datatype */
                typentry = lookup_type_cache(sortcoltype,
                                             TYPECACHE_LT_OPR | TYPECACHE_GT_OPR);
                if (srt->sortop == typentry->lt_opr)
                {
                        appendStringInfoString(buf, " ASC");
                }
                else
                {
                        appendStringInfoString(buf, " DESC");
                }
        }
}

/*
 * Print the representation of a parameter to be sent to the remote side.
 *
 * Note: we always label the Param's type explicitly rather than relying on
 * transmitting a numeric type OID in PQexecParams().  This allows us to
 * avoid assuming that types have the same OIDs on the remote side as they
 * do locally --- they need only have the same names.
 */
static void
printRemoteParam(int paramindex, Oid paramtype, int32 paramtypmod,
                 deparse_expr_cxt *context)
{
        StringInfo	buf = context->buf;
        appendStringInfo(buf, "?");
}

/*
 * Print the representation of a placeholder for a parameter that will be
 * sent to the remote side at execution time.
 *
 * This is used when we're just trying to EXPLAIN the remote query.
 * We don't have the actual value of the runtime parameter yet, and we don't
 * want the remote planner to generate a plan that depends on such a value
 * anyway.  Thus, we can't do something simple like "$1::paramtype".
 * Instead, we emit "((SELECT null::paramtype)::paramtype)".
 * In all extant versions of Postgres, the planner will see that as an unknown
 * constant value, which is what we want.  This might need adjustment if we
 * ever make the planner flatten scalar subqueries.  Note: the reason for the
 * apparently useless outer cast is to ensure that the representation as a
 * whole will be parsed as an a_expr and not a select_with_parens; the latter
 * would do the wrong thing in the context "x = ANY(...)".
 */
static void
printRemotePlaceholder(Oid paramtype, int32 paramtypmod,
                       deparse_expr_cxt *context)
{
}

/*
 * Deparse GROUP BY clause.
 */
static void
appendGroupByClause(List *tlist, deparse_expr_cxt *context)
{
        StringInfo	buf = context->buf;
        Query	   *query = context->root->parse;
        ListCell   *lc;
        bool		first = true;

        /* Nothing to be done, if there's no GROUP BY clause in the query. */
        if (!query->groupClause)
        {
                return;
        }

        appendStringInfoString(buf, " GROUP BY ");

        /*
         * Queries with grouping sets are not pushed down, so we don't expect
         * grouping sets here.
         */
        Assert(!query->groupingSets);

        foreach (lc, query->groupClause)
        {
                SortGroupClause *grp = (SortGroupClause *) lfirst(lc);

                if (!first)
                {
                        appendStringInfoString(buf, ", ");
                }
                first = false;

                deparseSortGroupClause(grp->tleSortGroupRef, tlist, true, context);
        }
}

/*
 * Deparse ORDER BY clause according to the given pathkeys for given base
 * relation. From given pathkeys expressions belonging entirely to the given
 * base relation are obtained and deparsed.
 */
static void
appendOrderByClause(List *pathkeys, deparse_expr_cxt *context)
{
        ListCell   *lcell;
        int			nestlevel;
        char	   *delim = " ";
        RelOptInfo *baserel = context->scanrel;
        StringInfo	buf = context->buf;

        /* Make sure any constants in the exprs are printed portably */
        nestlevel = set_transmission_modes();

        appendStringInfoString(buf, " ORDER BY");
        foreach (lcell, pathkeys)
        {
                PathKey    *pathkey = lfirst(lcell);
                Expr	   *em_expr;

                em_expr = find_em_expr_for_rel(pathkey->pk_eclass, baserel);
                Assert(em_expr != NULL);

                appendStringInfoString(buf, delim);
                deparseExpr(em_expr, context);
                if (pathkey->pk_strategy == BTLessStrategyNumber)
                {
                        appendStringInfoString(buf, " ASC");
                }
                else
                {
                        appendStringInfoString(buf, " DESC");
                }

                delim = ", ";
        }
        reset_transmission_modes(nestlevel);
}

/*
 * appendFunctionName
 *		Deparses function name from given function oid.
 */
static void
appendFunctionName(Oid funcid, deparse_expr_cxt *context)
{
        StringInfo	buf = context->buf;
        HeapTuple	proctup;
        Form_pg_proc procform;
        const char *proname;

        proctup = SearchSysCache1(PROCOID, ObjectIdGetDatum(funcid));
        if (!HeapTupleIsValid(proctup))
        {
                elog(ERROR, "cache lookup failed for function %u", funcid);
        }
        procform = (Form_pg_proc) GETSTRUCT(proctup);

        /* Print schema name only if it's not pg_catalog */
        if (procform->pronamespace != PG_CATALOG_NAMESPACE)
        {
                const char *schemaname;

                schemaname = get_namespace_name(procform->pronamespace);
                appendStringInfo(buf, "%s.", quote_identifier(schemaname));
        }

        /* Always print the function name */
        proname = NameStr(procform->proname);
        appendStringInfoString(buf, quote_identifier(proname));

        ReleaseSysCache(proctup);
}

/*
 * Appends a sort or group clause.
 *
 * Like get_rule_sortgroupclause(), returns the expression tree, so caller
 * need not find it again.
 */
static Node *
deparseSortGroupClause(Index ref, List *tlist, bool force_colno,
                       deparse_expr_cxt *context)
{
        StringInfo	buf = context->buf;
        TargetEntry *tle;
        Expr	   *expr;

        tle = get_sortgroupref_tle(ref, tlist);
        expr = tle->expr;

        if (expr && IsA(expr, Const))
        {
                /*
                 * Force a typecast here so that we don't emit something like "GROUP
                 * BY 2", which will be misconstrued as a column position rather than
                 * a constant.
                 */
                deparseConst((Const *) expr, context, 1);
        }
        else if (!expr || IsA(expr, Var))
        {
                deparseExpr(expr, context);
        }
        else
        {
                /* Always parenthesize the expression. */
                appendStringInfoChar(buf, '(');
                deparseExpr(expr, context);
                appendStringInfoChar(buf, ')');
        }

        return (Node *) expr;
}


/*
 * Returns true if given Var is deparsed as a subquery output column, in
 * which case, *relno and *colno are set to the IDs for the relation and
 * column alias to the Var provided by the subquery.
 */
static bool
is_subquery_var(Var *node, RelOptInfo *foreignrel, int *relno, int *colno)
{
        CHFdwRelationInfo *fpinfo = (CHFdwRelationInfo *) foreignrel->fdw_private;
        RelOptInfo *outerrel = fpinfo->outerrel;
        RelOptInfo *innerrel = fpinfo->innerrel;

        /* Should only be called in these cases. */
        Assert(IS_SIMPLE_REL(foreignrel) || IS_JOIN_REL(foreignrel));

        /*
         * If the given relation isn't a join relation, it doesn't have any lower
         * subqueries, so the Var isn't a subquery output column.
         */
        if (!IS_JOIN_REL(foreignrel))
        {
                return false;
        }

        /*
         * If the Var doesn't belong to any lower subqueries, it isn't a subquery
         * output column.
         */
        if (!bms_is_member(node->varno, fpinfo->lower_subquery_rels))
        {
                return false;
        }

        if (bms_is_member(node->varno, outerrel->relids))
        {
                /*
                 * If outer relation is deparsed as a subquery, the Var is an output
                 * column of the subquery; get the IDs for the relation/column alias.
                 */
                if (fpinfo->make_outerrel_subquery)
                {
                        get_relation_column_alias_ids(node, outerrel, relno, colno);
                        return true;
                }

                /* Otherwise, recurse into the outer relation. */
                return is_subquery_var(node, outerrel, relno, colno);
        }
        else
        {
                Assert(bms_is_member(node->varno, innerrel->relids));

                /*
                 * If inner relation is deparsed as a subquery, the Var is an output
                 * column of the subquery; get the IDs for the relation/column alias.
                 */
                if (fpinfo->make_innerrel_subquery)
                {
                        get_relation_column_alias_ids(node, innerrel, relno, colno);
                        return true;
                }

                /* Otherwise, recurse into the inner relation. */
                return is_subquery_var(node, innerrel, relno, colno);
        }
}

/*
 * Get the IDs for the relation and column alias to given Var belonging to
 * given relation, which are returned into *relno and *colno.
 */
static void
get_relation_column_alias_ids(Var *node, RelOptInfo *foreignrel,
                              int *relno, int *colno)
{
        CHFdwRelationInfo *fpinfo = (CHFdwRelationInfo *) foreignrel->fdw_private;
        int			i;
        ListCell   *lc;

        /* Get the relation alias ID */
        *relno = fpinfo->relation_index;

        /* Get the column alias ID */
        i = 1;
        foreach (lc, foreignrel->reltarget->exprs)
        {
                if (equal(lfirst(lc), (Node *) node))
                {
                        *colno = i;
                        return;
                }
                i++;
        }

        /* Shouldn't get here */
        elog(ERROR, "unexpected expression in subquery output");
}