From f595117e24a79db6072979ab5a757431fd17232f Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter@eisentraut.org>
Date: Tue, 14 Jan 2020 13:09:31 +0100
Subject: ALTER TABLE ... ALTER COLUMN ... DROP EXPRESSION

Add an ALTER TABLE subcommand for dropping the generated property from
a column, per SQL standard.

Reviewed-by: Sergei Kornilov <sk@zsrv.org>
Discussion: https://www.postgresql.org/message-id/flat/2f7f1d9c-946e-0453-d841-4f38eb9d69b6%402ndquadrant.com
---
 doc/src/sgml/ref/alter_table.sgml | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

(limited to 'doc/src')

diff --git a/doc/src/sgml/ref/alter_table.sgml b/doc/src/sgml/ref/alter_table.sgml
index 8403c797e2e..4bf449587cc 100644
--- a/doc/src/sgml/ref/alter_table.sgml
+++ b/doc/src/sgml/ref/alter_table.sgml
@@ -46,6 +46,7 @@ ALTER TABLE [ IF EXISTS ] <replaceable class="parameter">name</replaceable>
     ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> SET DEFAULT <replaceable class="parameter">expression</replaceable>
     ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> DROP DEFAULT
     ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> { SET | DROP } NOT NULL
+    ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> DROP EXPRESSION [ IF EXISTS ]
     ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> ADD GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ ( <replaceable>sequence_options</replaceable> ) ]
     ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> { SET GENERATED { ALWAYS | BY DEFAULT } | SET <replaceable>sequence_option</replaceable> | RESTART [ [ WITH ] <replaceable class="parameter">restart</replaceable> ] } [...]
     ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> DROP IDENTITY [ IF EXISTS ]
@@ -241,6 +242,23 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
     </listitem>
    </varlistentry>
 
+   <varlistentry>
+    <term><literal>DROP EXPRESSION [ IF EXISTS ]</literal></term>
+    <listitem>
+     <para>
+      This form turns a stored generated column into a normal base column.
+      Existing data in the columns is retained, but future changes will no
+      longer apply the generation expression.
+     </para>
+
+     <para>
+      If <literal>DROP EXPRESSION IF EXISTS</literal> is specified and the
+      column is not a stored generated column, no error is thrown.  In this
+      case a notice is issued instead.
+     </para>
+    </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term><literal>ADD GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY</literal></term>
     <term><literal>SET GENERATED { ALWAYS | BY DEFAULT }</literal></term>
-- 
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