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author | Simon Riggs <simon@2ndQuadrant.com> | 2018-04-03 09:28:16 +0100 |
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committer | Simon Riggs <simon@2ndQuadrant.com> | 2018-04-03 09:28:16 +0100 |
commit | d204ef63776b8a00ca220adec23979091564e465 (patch) | |
tree | 5fa3d403db1d0377d85d20b9afb949c58855a37f /doc/src | |
parent | aa5877bb26347c58a34aee4e460eb1e1123bb096 (diff) | |
download | postgresql-d204ef63776b8a00ca220adec23979091564e465.tar.gz |
MERGE SQL Command following SQL:2016
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
Diffstat (limited to 'doc/src')
-rw-r--r-- | doc/src/sgml/libpq.sgml | 8 | ||||
-rw-r--r-- | doc/src/sgml/mvcc.sgml | 28 | ||||
-rw-r--r-- | doc/src/sgml/plpgsql.sgml | 3 | ||||
-rw-r--r-- | doc/src/sgml/ref/allfiles.sgml | 1 | ||||
-rw-r--r-- | doc/src/sgml/ref/create_policy.sgml | 7 | ||||
-rw-r--r-- | doc/src/sgml/ref/insert.sgml | 11 | ||||
-rw-r--r-- | doc/src/sgml/reference.sgml | 1 | ||||
-rw-r--r-- | doc/src/sgml/trigger.sgml | 20 |
8 files changed, 73 insertions, 6 deletions
diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml index 943adfef77..8729ccd5c5 100644 --- a/doc/src/sgml/libpq.sgml +++ b/doc/src/sgml/libpq.sgml @@ -3917,9 +3917,11 @@ char *PQcmdTuples(PGresult *res); <structname>PGresult</structname>. This function can only be used following the execution of a <command>SELECT</command>, <command>CREATE TABLE AS</command>, <command>INSERT</command>, <command>UPDATE</command>, <command>DELETE</command>, - <command>MOVE</command>, <command>FETCH</command>, or <command>COPY</command> statement, - or an <command>EXECUTE</command> of a prepared query that contains an - <command>INSERT</command>, <command>UPDATE</command>, or <command>DELETE</command> statement. + <command>MERGE</command>, <command>MOVE</command>, <command>FETCH</command>, + or <command>COPY</command> statement, or an <command>EXECUTE</command> of a + prepared query that contains an <command>INSERT</command>, + <command>UPDATE</command>, <command>DELETE</command> + or <command>MERGE</command> statement. If the command that generated the <structname>PGresult</structname> was anything else, <function>PQcmdTuples</function> returns an empty string. The caller should not free the return value directly. It will be freed when diff --git a/doc/src/sgml/mvcc.sgml b/doc/src/sgml/mvcc.sgml index 24613e3c75..0e3e89af56 100644 --- a/doc/src/sgml/mvcc.sgml +++ b/doc/src/sgml/mvcc.sgml @@ -423,6 +423,31 @@ COMMIT; </para> <para> + The <command>MERGE</command> allows the user to specify various combinations + of <command>INSERT</command>, <command>UPDATE</command> or + <command>DELETE</command> subcommands. A <command>MERGE</command> command + with both <command>INSERT</command> and <command>UPDATE</command> + subcommands looks similar to <command>INSERT</command> with an + <literal>ON CONFLICT DO UPDATE</literal> clause but does not guarantee + that either <command>INSERT</command> and <command>UPDATE</command> will occur. + + If MERGE attempts an UPDATE or DELETE and the row is concurrently updated + but the join condition still passes for the current target and the current + source tuple, then MERGE will behave the same as the UPDATE or DELETE commands + and perform its action on the latest version of the row, using standard + EvalPlanQual. MERGE actions can be conditional, so conditions must be + re-evaluated on the latest row, starting from the first action. + + On the other hand, if the row is concurrently updated or deleted so that + the join condition fails, then MERGE will execute a NOT MATCHED action, if it + exists and the AND WHEN qual evaluates to true. + + If MERGE attempts an INSERT and a unique index is present and a duplicate + row is concurrently inserted then a uniqueness violation is raised. MERGE + does not attempt to avoid the ERROR by attempting an UPDATE. + </para> + + <para> Because Read Committed mode starts each command with a new snapshot that includes all transactions committed up to that instant, subsequent commands in the same transaction will see the effects @@ -900,7 +925,8 @@ ERROR: could not serialize access due to read/write dependencies among transact <para> The commands <command>UPDATE</command>, - <command>DELETE</command>, and <command>INSERT</command> + <command>DELETE</command>, <command>INSERT</command> and + <command>MERGE</command> acquire this lock mode on the target table (in addition to <literal>ACCESS SHARE</literal> locks on any other referenced tables). In general, this lock mode will be acquired by any diff --git a/doc/src/sgml/plpgsql.sgml b/doc/src/sgml/plpgsql.sgml index 5b2aac618e..59f6112b07 100644 --- a/doc/src/sgml/plpgsql.sgml +++ b/doc/src/sgml/plpgsql.sgml @@ -1246,7 +1246,7 @@ EXECUTE format('SELECT count(*) FROM %I ' </programlisting> Another restriction on parameter symbols is that they only work in <command>SELECT</command>, <command>INSERT</command>, <command>UPDATE</command>, and - <command>DELETE</command> commands. In other statement + <command>DELETE</command> and <command>MERGE</command> commands. In other statement types (generically called utility statements), you must insert values textually even if they are just data values. </para> @@ -1529,6 +1529,7 @@ GET DIAGNOSTICS integer_var = ROW_COUNT; <listitem> <para> <command>UPDATE</command>, <command>INSERT</command>, and <command>DELETE</command> + and <command>MERGE</command> statements set <literal>FOUND</literal> true if at least one row is affected, false if no row is affected. </para> diff --git a/doc/src/sgml/ref/allfiles.sgml b/doc/src/sgml/ref/allfiles.sgml index 22e6893211..4e01e5641c 100644 --- a/doc/src/sgml/ref/allfiles.sgml +++ b/doc/src/sgml/ref/allfiles.sgml @@ -159,6 +159,7 @@ Complete list of usable sgml source files in this directory. <!ENTITY load SYSTEM "load.sgml"> <!ENTITY lock SYSTEM "lock.sgml"> <!ENTITY move SYSTEM "move.sgml"> +<!ENTITY merge SYSTEM "merge.sgml"> <!ENTITY notify SYSTEM "notify.sgml"> <!ENTITY prepare SYSTEM "prepare.sgml"> <!ENTITY prepareTransaction SYSTEM "prepare_transaction.sgml"> diff --git a/doc/src/sgml/ref/create_policy.sgml b/doc/src/sgml/ref/create_policy.sgml index 0e35b0ef43..32f39a48ba 100644 --- a/doc/src/sgml/ref/create_policy.sgml +++ b/doc/src/sgml/ref/create_policy.sgml @@ -94,6 +94,13 @@ CREATE POLICY <replaceable class="parameter">name</replaceable> ON <replaceable exist, a <quote>default deny</quote> policy is assumed, so that no rows will be visible or updatable. </para> + + <para> + No separate policy exists for <command>MERGE</command>. Instead policies + defined for <literal>SELECT</literal>, <literal>INSERT</literal>, + <literal>UPDATE</literal> and <literal>DELETE</literal> are applied + while executing MERGE, depending on the actions that are activated. + </para> </refsect1> <refsect1> diff --git a/doc/src/sgml/ref/insert.sgml b/doc/src/sgml/ref/insert.sgml index 62e142fd8e..da294aaa46 100644 --- a/doc/src/sgml/ref/insert.sgml +++ b/doc/src/sgml/ref/insert.sgml @@ -579,6 +579,13 @@ INSERT <replaceable>oid</replaceable> <replaceable class="parameter">count</repl is a partition, an error will occur if one of the input rows violates the partition constraint. </para> + + <para> + You may also wish to consider using <command>MERGE</command>, since that + allows mixed <command>INSERT</command>, <command>UPDATE</command> and + <command>DELETE</command> within a single statement. + See <xref linkend="sql-merge"/>. + </para> </refsect1> <refsect1> @@ -749,7 +756,9 @@ INSERT INTO distributors (did, dname) VALUES (10, 'Conrad International') Also, the case in which a column name list is omitted, but not all the columns are filled from the <literal>VALUES</literal> clause or <replaceable>query</replaceable>, - is disallowed by the standard. + is disallowed by the standard. If you prefer a more SQL Standard + conforming statement than <literal>ON CONFLICT</literal>, see + <xref linkend="sql-merge"/>. </para> <para> diff --git a/doc/src/sgml/reference.sgml b/doc/src/sgml/reference.sgml index d27fb414f7..ef2270c467 100644 --- a/doc/src/sgml/reference.sgml +++ b/doc/src/sgml/reference.sgml @@ -186,6 +186,7 @@ &listen; &load; &lock; + &merge; &move; ¬ify; &prepare; diff --git a/doc/src/sgml/trigger.sgml b/doc/src/sgml/trigger.sgml index c43dbc9786..cce58fbf1d 100644 --- a/doc/src/sgml/trigger.sgml +++ b/doc/src/sgml/trigger.sgml @@ -183,6 +183,26 @@ </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 triggers can return a table row (a value of |