Allow specifying column list for foreign key ON DELETE SET actions

Extend the foreign key ON DELETE actions SET NULL and SET DEFAULT by
allowing the specification of a column list, like

    CREATE TABLE posts (
        ...
        FOREIGN KEY (tenant_id, author_id) REFERENCES users ON DELETE SET NULL (author_id)
    );

If a column list is specified, only those columns are set to
null/default, instead of all the columns in the foreign-key
constraint.

This is useful for multitenant or sharded schemas, where the tenant or
shard ID is included in the primary key of all tables but shouldn't be
set to null.

Author: Paul Martinez <paulmtz@google.com>
Discussion: https://www.postgresql.org/message-id/flat/CACqFVBZQyMYJV=njbSMxf+rbDHpx=W=B7AEaMKn8dWn9OZJY7w@mail.gmail.com

1 files changed, 19 insertions, 5 deletions

diff --git a/doc/src/sgml/ref/create_table.sgml b/doc/src/sgml/ref/create_table.sgml
index 57d51a676a7..b97bb9ded15 100644
--- a/doc/src/sgml/ref/create_table.sgml
+++ b/doc/src/sgml/ref/create_table.sgml
@@ -108,7 +108,7 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
 
 <phrase><replaceable class="parameter">referential_action</replaceable> in a <literal>FOREIGN KEY</literal>/<literal>REFERENCES</literal> constraint is:</phrase>
 
-{ NO ACTION | RESTRICT | CASCADE | SET NULL | SET DEFAULT }
+{ NO ACTION | RESTRICT | CASCADE | SET NULL [ ( <replaceable class="parameter">column_name</replaceable> [, ... ] ) ] | SET DEFAULT [ ( <replaceable class="parameter">column_name</replaceable> [, ... ] ) ] }
 </synopsis>
 
  </refsynopsisdiv>
@@ -1169,19 +1169,23 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
        </varlistentry>
 
        <varlistentry>
-        <term><literal>SET NULL</literal></term>
+        <term><literal>SET NULL [ ( <replaceable>column_name</replaceable> [, ... ] ) ]</literal></term>
         <listitem>
          <para>
-          Set the referencing column(s) to null.
+          Set all of the referencing columns, or a specified subset of the
+          referencing columns, to null. A subset of columns can only be
+          specified for <literal>ON DELETE</literal> actions.
          </para>
         </listitem>
        </varlistentry>
 
        <varlistentry>
-        <term><literal>SET DEFAULT</literal></term>
+        <term><literal>SET DEFAULT [ ( <replaceable>column_name</replaceable> [, ... ] ) ]</literal></term>
         <listitem>
          <para>
-          Set the referencing column(s) to their default values.
+          Set all of the referencing columns, or a specified subset of the
+          referencing columns, to their default values. A subset of columns
+          can only be specified for <literal>ON DELETE</literal> actions.
           (There must be a row in the referenced table matching the default
           values, if they are not null, or the operation will fail.)
          </para>
@@ -2224,6 +2228,16 @@ CREATE TABLE cities_partdef
   </refsect2>
 
   <refsect2>
+   <title>Foreign-Key Constraint Actions</title>
+
+   <para>
+    The ability to specify column lists in the foreign-key actions
+    <literal>SET DEFAULT</literal> and <literal>SET NULL</literal> is a
+    <productname>PostgreSQL</productname> extension.
+   </para>
+  </refsect2>
+
+  <refsect2>
    <title><literal>NULL</literal> <quote>Constraint</quote></title>
 
    <para>