Add Postgre function: DATE_TRUNC

src/backend/postgres/query.rs

@@ -124,6 +124,7 @@ impl QueryBuilder for PostgresQueryBuilder {
                     PgFunction::GenRandomUUID => "GEN_RANDOM_UUID",
                     PgFunction::JsonBuildObject => "JSON_BUILD_OBJECT",
                     PgFunction::JsonAgg => "JSON_AGG",
+                    PgFunction::DateTrunc => "DATE_TRUNC",
                     #[cfg(feature = "postgres-array")]
                     PgFunction::Any => "ANY",
                     #[cfg(feature = "postgres-array")]

src/extension/postgres/func.rs

@@ -1,6 +1,6 @@
 //! For calling built-in Postgres SQL functions.
 
-use crate::{expr::*, func::*};
+use crate::{expr::*, func::*, PgDateTruncUnit};
 
 /// Functions
 #[derive(Debug, Clone, PartialEq)]
@@ -16,6 +16,7 @@ pub enum PgFunction {
     GenRandomUUID,
     JsonBuildObject,
     JsonAgg,
+    DateTrunc,
     #[cfg(feature = "postgres-array")]
     Any,
     #[cfg(feature = "postgres-array")]
@@ -384,6 +385,45 @@ impl PgFunc {
         FunctionCall::new(Function::PgFunction(PgFunction::JsonBuildObject)).args(args)
     }
 
+    /// Call the `DATE_TRUNC` function. Postgres only.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use sea_query::{tests_cfg::*, *};
+    ///
+    /// let query = Query::select()
+    ///     .expr(PgFunc::date_trunc(
+    ///         PgDateTruncUnit::Day,
+    ///         Expr::val("2020-01-01"),
+    ///     ))
+    ///     .to_owned();
+    ///
+    /// assert_eq!(
+    ///     query.to_string(PostgresQueryBuilder),
+    ///     r#"SELECT DATE_TRUNC('day', '2020-01-01')"#
+    /// );
+    ///
+    /// let query = Query::select()
+    ///     .expr(PgFunc::date_trunc(
+    ///         PgDateTruncUnit::Microseconds,
+    ///         Expr::val("2020-01-01"),
+    ///     ))
+    ///     .to_owned();
+    ///
+    /// assert_eq!(
+    ///     query.to_string(PostgresQueryBuilder),
+    ///     r#"SELECT DATE_TRUNC('microseconds', '2020-01-01')"#
+    /// );
+    /// ```
+    pub fn date_trunc<T>(unit: PgDateTruncUnit, expr: T) -> FunctionCall
+    where
+        T: Into<SimpleExpr>,
+    {
+        FunctionCall::new(Function::PgFunction(PgFunction::DateTrunc))
+            .args([Expr::val(unit.to_string()).into(), expr.into()])
+    }
+
     /// Call the `JSON_AGG` function. Postgres only.
     ///
     /// # Examples

src/table/column.rs

@@ -1,3 +1,5 @@
+use std::fmt;
+
 use crate::{expr::*, types::*};
 
 /// Specification of a table column
@@ -200,6 +202,45 @@ pub enum PgInterval {
     MinuteToSecond,
 }
 
+// All possible inputs to DATE_TRUNC (https://www.postgresql.org/docs/current/functions-datetime.html#FUNCTIONS-DATETIME-TRUNC)
+#[derive(Debug, Clone, Eq, PartialEq)]
+pub enum PgDateTruncUnit {
+    Microseconds,
+    Milliseconds,
+    Second,
+    Minute,
+    Hour,
+    Day,
+    Week,
+    Month,
+    Quarter,
+    Year,
+    Decade,
+    Century,
+    Millennium,
+}
+
+impl fmt::Display for PgDateTruncUnit {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let text = match self {
+            PgDateTruncUnit::Microseconds => "microseconds",
+            PgDateTruncUnit::Milliseconds => "milliseconds",
+            PgDateTruncUnit::Second => "second",
+            PgDateTruncUnit::Minute => "minute",
+            PgDateTruncUnit::Hour => "hour",
+            PgDateTruncUnit::Day => "day",
+            PgDateTruncUnit::Week => "week",
+            PgDateTruncUnit::Month => "month",
+            PgDateTruncUnit::Quarter => "quarter",
+            PgDateTruncUnit::Year => "year",
+            PgDateTruncUnit::Decade => "decade",
+            PgDateTruncUnit::Century => "century",
+            PgDateTruncUnit::Millennium => "millennium",
+        };
+        write!(f, "{}", text)
+    }
+}
+
 impl ColumnDef {
     /// Construct a table column
     pub fn new<T>(name: T) -> Self