new doc

Author: digoal

201908/20190813_01.md

@@ -0,0 +1,118 @@
+## PostgreSQL Oracle 兼容性之 dump chars's byte stream - decode  
+          
+### 作者          
+digoal          
+          
+### 日期          
+2019-08-13         
+          
+### 标签          
+PostgreSQL , 字符串字节流 , dump      
+          
+----          
+          
+## 背景          
+导出字符串的长度，显示逐个字节。  
+  
+oracle dump用法如下  
+  
+https://docs.oracle.com/cd/B28359_01/server.111/b28286/functions048.htm  
+  
+```  
+Examples  
+  
+The following examples show how to extract dump information from a string expression and a column:  
+  
+SELECT DUMP('abc', 1016)  
+   FROM DUAL;  
+  
+DUMP('ABC',1016)                            
+------------------------------------------   
+Typ=96 Len=3 CharacterSet=WE8DEC: 61,62,63   
+SELECT DUMP(last_name, 8, 3, 2) "OCTAL"  
+   FROM employees  
+   WHERE last_name = 'Hunold'  
+   ORDER BY employee_id;  
+  
+OCTAL  
+-------------------------------------------------------------------  
+Typ=1 Len=6: 156,157  
+  
+SELECT DUMP(last_name, 10, 3, 2) "ASCII"  
+   FROM employees  
+   WHERE last_name = 'Hunold'  
+   ORDER BY employee_id;  
+  
+ASCII  
+--------------------------------------------------------------------  
+Typ=1 Len=6: 110,111  
+```  
+  
+  
+## PG dump实现方法  
+借助PG的类型转换，自定义一个sql函数即可。  
+  
+```  
+postgres=# show bytea_output ;  
+ bytea_output   
+--------------  
+ hex  
+(1 row)  
+  
+postgres=# select 'nihao 德哥'::bytea;  
+           bytea              
+----------------------------  
+ \x6e6968616f20e5beb7e593a5  
+(1 row)  
+```  
+  
+```  
+postgres=#   
+select format('Len=%s ', len) || string_agg(res,',') from   
+  (select to_hex(get_byte(info::bytea, generate_series(0,len-1))) res,len from   
+    (select info,octet_length(info) len from   
+      (values('nihao中国digoal德哥')) t(info)  
+    )t   
+  )t   
+group by len;  
+                                  ?column?                                     
+-----------------------------------------------------------------------------  
+ Len=23 6e,69,68,61,6f,e4,b8,ad,e5,9b,bd,64,69,67,6f,61,6c,e5,be,b7,e5,93,a5  
+(1 row)  
+```  
+  
+写成函数如下  
+  
+```  
+create or replace function dump(text) returns text as $$  
+  select format('Len=%s ', len) || string_agg(res,',') from   
+    (select to_hex(get_byte(info::bytea, generate_series(0,len-1))) res,len from   
+      (select info,octet_length(info) len from   
+        (values($1)) t(info)  
+      )t   
+    )t   
+  group by len;  
+$$ language sql strict immutable;  
+```  
+  
+使用dump函数将导出字符串的字节流  
+  
+```  
+postgres=# select dump(';nihao中国digoal德哥');  
+                                      dump                                        
+--------------------------------------------------------------------------------  
+ Len=24 3b,6e,69,68,61,6f,e4,b8,ad,e5,9b,bd,64,69,67,6f,61,6c,e5,be,b7,e5,93,a5  
+(1 row)  
+```  
+  
+简单好用。    
+  
+  
+<a rel="nofollow" href="http://info.flagcounter.com/h9V1"  ><img src="http://s03.flagcounter.com/count/h9V1/bg_FFFFFF/txt_000000/border_CCCCCC/columns_2/maxflags_12/viewers_0/labels_0/pageviews_0/flags_0/"  alt="Flag Counter"  border="0"  ></a>  
+  
+  
+## [digoal's 大量PostgreSQL文章入口](https://github.com/digoal/blog/blob/master/README.md "22709685feb7cab07d30f30387f0a9ae")
+  
+  
+## [免费领取阿里云RDS PostgreSQL实例、ECS虚拟机](https://free.aliyun.com/ "57258f76c37864c6e6d23383d05714ea")
+  

201908/readme.md

@@ -2,6 +2,7 @@
 
 ### 文章列表  
 ----  
+##### 20190813_01.md   [《PostgreSQL Oracle 兼容性之 dump chars's byte stream - decode》](20190813_01.md)  
 ##### 20190812_02.md   [《PostgreSQL 数据库资源限制 + HOOK(limit guc) - 降低攻击伤害、自动SQL优化等》](20190812_02.md)  
 ##### 20190812_01.md   [《chrome清理缓存socket, dns》](20190812_01.md)  
 ##### 20190807_01.md   [《freeze 事务号将保留到实例中的最老事务, 年龄降不下来快看最老事务(2pc,long query,long xact)》](20190807_01.md)  

README.md

@@ -54,6 +54,7 @@ digoal's|PostgreSQL|文章|归类
 
 ### 所有文档如下  
 ----  
+##### 201908/20190813_01.md   [《PostgreSQL Oracle 兼容性之 dump chars's byte stream - decode》](201908/20190813_01.md)  
 ##### 201908/20190812_02.md   [《PostgreSQL 数据库资源限制 + HOOK(limit guc) - 降低攻击伤害、自动SQL优化等》](201908/20190812_02.md)  
 ##### 201908/20190812_01.md   [《chrome清理缓存socket, dns》](201908/20190812_01.md)  
 ##### 201908/20190807_01.md   [《freeze 事务号将保留到实例中的最老事务, 年龄降不下来快看最老事务(2pc,long query,long xact)》](201908/20190807_01.md)