PostgreSQL 15 preview - 支持 MERGE INTO 语法

原创 digoal 2022-01-20

2008

作者

digoal

日期

2022-03-29

Add support for MERGE SQL command  
author  Alvaro Herrera <alvherre@alvh.no-ip.org>      
Mon, 28 Mar 2022 14:45:58 +0000 (16:45 +0200)  
committer   Alvaro Herrera <alvherre@alvh.no-ip.org>      
Mon, 28 Mar 2022 14:47:48 +0000 (16:47 +0200)  
commit  7103ebb7aae8ab8076b7e85f335ceb8fe799097c  
tree    0bc2faf176b58d2546de40c3c36d93a4cdf1aafe    tree  
parent  ae63017bdb316b16a9f201b10f1221598111d6c5    commit | diff  
Add support for MERGE SQL command  
MERGE performs actions that modify rows in the target table using a  
source table or query. MERGE provides a single SQL statement that can  
conditionally INSERT/UPDATE/DELETE rows -- a task that would otherwise  
require multiple PL statements.  For example,  
MERGE INTO target AS t  
USING source AS s  
ON t.tid = s.sid  
WHEN MATCHED AND t.balance > s.delta THEN  
  UPDATE SET balance = t.balance - s.delta  
WHEN MATCHED THEN  
  DELETE  
WHEN NOT MATCHED AND s.delta > 0 THEN  
  INSERT VALUES (s.sid, s.delta)  
WHEN NOT MATCHED THEN  
  DO NOTHING;  
MERGE works with regular tables, partitioned tables and inheritance  
hierarchies, including column and row security enforcement, as well as  
support for row and statement triggers and transition tables therein.  
MERGE is optimized for OLTP and is parameterizable, though also useful  
for large scale ETL/ELT. MERGE is not intended to be used in preference  
to existing single SQL commands for INSERT, UPDATE or DELETE since there  
is some overhead.  MERGE can be used from PL/pgSQL.  
MERGE does not support targetting updatable views or foreign tables, and  
RETURNING clauses are not allowed either.  These limitations are likely  
fixable with sufficient effort.  Rewrite rules are also not supported,  
but it's not clear that we'd want to support them.  
Author: Pavan Deolasee <pavan.deolasee@gmail.com>  
Author: Álvaro Herrera <alvherre@alvh.no-ip.org>  
Author: Amit Langote <amitlangote09@gmail.com>  
Author: Simon Riggs <simon.riggs@enterprisedb.com>  
Reviewed-by: Peter Eisentraut <peter.eisentraut@enterprisedb.com>  
Reviewed-by: Andres Freund <andres@anarazel.de> (earlier versions)  
Reviewed-by: Peter Geoghegan <pg@bowt.ie> (earlier versions)  
Reviewed-by: Robert Haas <robertmhaas@gmail.com> (earlier versions)  
Reviewed-by: Japin Li <japinli@hotmail.com>  
Reviewed-by: Justin Pryzby <pryzby@telsasoft.com>  
Reviewed-by: Tomas Vondra <tomas.vondra@enterprisedb.com>  
Reviewed-by: Zhihong Yu <zyu@yugabyte.com>  
Discussion: https://postgr.es/m/CANP8+jKitBSrB7oTgT9CY2i1ObfOt36z0XMraQc+Xrz8QB0nXA@mail.gmail.com  
Discussion: https://postgr.es/m/CAH2-WzkJdBuxj9PO=2QaO9-3h3xGbQPZ34kJH=HukRekwM-GZg@mail.gmail.com  
Discussion: https://postgr.es/m/20201231134736.GA25392@alvherre.pgsql

MERGE  
MERGE — conditionally insert, update, or delete rows of a table  
Synopsis  
[ WITH with_query [, ...] ]  
MERGE INTO target_table_name [ [ AS ] target_alias ]  
USING data_source ON join_condition  
when_clause [...]  
where data_source is  
{ source_table_name | ( source_query ) } [ [ AS ] source_alias ]  
and when_clause is  
{ WHEN MATCHED [ AND condition ] THEN { merge_update | merge_delete | DO NOTHING } |  
  WHEN NOT MATCHED [ AND condition ] THEN { merge_insert | DO NOTHING } }  
and merge_insert is  
INSERT [( column_name [, ...] )]  
[ OVERRIDING { SYSTEM | USER } VALUE ]  
{ VALUES ( { expression | DEFAULT } [, ...] ) | DEFAULT VALUES }  
and merge_update is  
UPDATE SET { column_name = { expression | DEFAULT } |  
             ( column_name [, ...] ) = ( { expression | DEFAULT } [, ...] ) } [, ...]  
and merge_delete is  
DELETE

例子:

https://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=src/test/regress/expected/merge.out;h=da8796986ff16b00546398fcb016c1b9e557abb9;hb=7103ebb7aae8ab8076b7e85f335ceb8fe799097c