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Add support for MERGE SQL command

Browse Source 
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
This commit is contained in:
Alvaro Herrera
2022-03-28 16:45:58 +02:00
parent ae63017bdb
commit 7103ebb7aa
95 changed files with 8726 additions and 167 deletions
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22
doc/src/sgml/trigger.sgml
View File

@@ -192,6 +192,28 @@
will be fired.
</para>
<para>
No separate triggers are defined for <command>MERGE</command>. Instead,
statement-level or row-level <command>UPDATE</command>,
<command>DELETE</command>, and <command>INSERT</command> triggers are fired
depending on (for statement-level triggers) what actions are specified in
the <command>MERGE</command> query and (for row-level triggers) what
actions are performed.
</para>
<para>
While running a <command>MERGE</command> command, statement-level
<literal>BEFORE</literal> and <literal>AFTER</literal> triggers are
fired for events specified in the actions of the <command>MERGE</command>
command, irrespective of whether or not the action is ultimately performed.
This is the same as an <command>UPDATE</command> statement that updates
no rows, yet statement-level triggers are fired.
The row-level triggers are fired only when a row is actually updated,
inserted or deleted. So it's perfectly legal that while statement-level
triggers are fired for certain types of action, no row-level triggers
are fired for the same kind of action.
</para>
<para>
Trigger functions invoked by per-statement triggers should always
return <symbol>NULL</symbol>. Trigger functions invoked by per-row