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Add OLD/NEW support to RETURNING in DML queries.

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This allows the RETURNING list of INSERT/UPDATE/DELETE/MERGE queries
to explicitly return old and new values by using the special aliases
"old" and "new", which are automatically added to the query (if not
already defined) while parsing its RETURNING list, allowing things
like:

  RETURNING old.colname, new.colname, ...

  RETURNING old.*, new.*

Additionally, a new syntax is supported, allowing the names "old" and
"new" to be changed to user-supplied alias names, e.g.:

  RETURNING WITH (OLD AS o, NEW AS n) o.colname, n.colname, ...

This is useful when the names "old" and "new" are already defined,
such as inside trigger functions, allowing backwards compatibility to
be maintained -- the interpretation of any existing queries that
happen to already refer to relations called "old" or "new", or use
those as aliases for other relations, is not changed.

For an INSERT, old values will generally be NULL, and for a DELETE,
new values will generally be NULL, but that may change for an INSERT
with an ON CONFLICT ... DO UPDATE clause, or if a query rewrite rule
changes the command type. Therefore, we put no restrictions on the use
of old and new in any DML queries.

Dean Rasheed, reviewed by Jian He and Jeff Davis.

Discussion: https://postgr.es/m/CAEZATCWx0J0-v=Qjc6gXzR=KtsdvAE7Ow=D=mu50AgOe+pvisQ@mail.gmail.com
This commit is contained in:
Dean Rasheed
2025-01-16 14:57:35 +00:00
parent 7407b2d48c
commit 80feb727c8
61 changed files with 2910 additions and 390 deletions
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40
doc/src/sgml/ref/delete.sgml
View File

@@ -25,7 +25,8 @@ PostgreSQL documentation
DELETE FROM [ ONLY ] <replaceable class="parameter">table_name</replaceable> [ * ] [ [ AS ] <replaceable class="parameter">alias</replaceable> ]
[ USING <replaceable class="parameter">from_item</replaceable> [, ...] ]
[ WHERE <replaceable class="parameter">condition</replaceable> | WHERE CURRENT OF <replaceable class="parameter">cursor_name</replaceable> ]
[ RETURNING { * | <replaceable class="parameter">output_expression</replaceable> [ [ AS ] <replaceable class="parameter">output_name</replaceable> ] } [, ...] ]
[ RETURNING [ WITH ( { OLD | NEW } AS <replaceable class="parameter">output_alias</replaceable> [, ...] ) ]
{ * | <replaceable class="parameter">output_expression</replaceable> [ [ AS ] <replaceable class="parameter">output_name</replaceable> ] } [, ...] ]
</synopsis>
</refsynopsisdiv>
@@ -160,6 +161,26 @@ DELETE FROM [ ONLY ] <replaceable class="parameter">table_name</replaceable> [ *
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">output_alias</replaceable></term>
<listitem>
<para>
An optional substitute name for <literal>OLD</literal> or
<literal>NEW</literal> rows in the <literal>RETURNING</literal> list.
</para>
<para>
By default, old values from the target table can be returned by writing
<literal>OLD.<replaceable class="parameter">column_name</replaceable></literal>
or <literal>OLD.*</literal>, and new values can be returned by writing
<literal>NEW.<replaceable class="parameter">column_name</replaceable></literal>
or <literal>NEW.*</literal>. When an alias is provided, these names are
hidden and the old or new rows must be referred to using the alias.
For example <literal>RETURNING WITH (OLD AS o, NEW AS n) o.*, n.*</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">output_expression</replaceable></term>
<listitem>
@@ -170,6 +191,23 @@ DELETE FROM [ ONLY ] <replaceable class="parameter">table_name</replaceable> [ *
or table(s) listed in <literal>USING</literal>.
Write <literal>*</literal> to return all columns.
</para>
<para>
A column name or <literal>*</literal> may be qualified using
<literal>OLD</literal> or <literal>NEW</literal>, or the corresponding
<replaceable class="parameter">output_alias</replaceable> for
<literal>OLD</literal> or <literal>NEW</literal>, to cause old or new
values to be returned. An unqualified column name, or
<literal>*</literal>, or a column name or <literal>*</literal> qualified
using the target table name or alias will return old values.
</para>
<para>
For a simple <command>DELETE</command>, all new values will be
<literal>NULL</literal>. However, if an <literal>ON DELETE</literal>
rule causes an <command>INSERT</command> or <command>UPDATE</command>
to be executed instead, the new values may be non-<literal>NULL</literal>.
</para>
</listitem>
</varlistentry>