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MERGE SQL Command following SQL:2016

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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 other require multiple PL statements.
e.g.

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 and partitioned tables, including
column and row security enforcement, as well as support for
row, statement and transition triggers.

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 statically from PL/pgSQL.

MERGE does not yet support inheritance, write rules,
RETURNING clauses, updatable views or foreign tables.
MERGE follows SQL Standard per the most recent SQL:2016.

Includes full tests and documentation, including full
isolation tests to demonstrate the concurrent behavior.

This version written from scratch in 2017 by Simon Riggs,
using docs and tests originally written in 2009. Later work
from Pavan Deolasee has been both complex and deep, leaving
the lead author credit now in his hands.
Extensive discussion of concurrency from Peter Geoghegan,
with thanks for the time and effort contributed.

Various issues reported via sqlsmith by Andreas Seltenreich

Authors: Pavan Deolasee, Simon Riggs
Reviewer: Peter Geoghegan, Amit Langote, Tomas Vondra, Simon Riggs

Discussion:
https://postgr.es/m/CANP8+jKitBSrB7oTgT9CY2i1ObfOt36z0XMraQc+Xrz8QB0nXA@mail.gmail.com
https://postgr.es/m/CAH2-WzkJdBuxj9PO=2QaO9-3h3xGbQPZ34kJH=HukRekwM-GZg@mail.gmail.com
This commit is contained in:
Simon Riggs
2018-04-03 09:28:16 +01:00
parent aa5877bb26
commit d204ef6377
82 changed files with 2600 additions and 165 deletions
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20
doc/src/sgml/trigger.sgml
View File

@@ -182,6 +182,26 @@
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 what actions are specified in the <command>MERGE</command> query
and what actions are activated.
</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 the action is finally activated or not. This is 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 type 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