From 7946f77220bb960e7ba5ed2a9dfb84ac3f926b2f Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Thu, 3 Aug 2006 20:57:06 +0000
Subject: [PATCH] Cause ALTER TABLE to perform ALTER COLUMN DROP DEFAULT
 operations during the DROP pass rather than the ADD_CONSTR pass.  On
 examining the code I think this was just an oversight rather than
 intentional, and it seems to satisfy the principle of least surprise better
 than the alternative solution that was discussed.  Add an example to the ref
 page showing how to do ALTER TYPE and update the default in one command.  Per
 gripe from Markus Bertheau that that wasn't possible.

---
 doc/src/sgml/ref/alter_table.sgml | 15 ++++++++++++++-
 src/backend/commands/tablecmds.c  |  4 ++--
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/doc/src/sgml/ref/alter_table.sgml b/doc/src/sgml/ref/alter_table.sgml
index c753eb6300..17b0f3667d 100644
--- a/doc/src/sgml/ref/alter_table.sgml
+++ b/doc/src/sgml/ref/alter_table.sgml
@@ -1,5 +1,5 @@
 <!--
-$PostgreSQL: pgsql/doc/src/sgml/ref/alter_table.sgml,v 1.87 2006/07/04 18:07:24 tgl Exp $
+$PostgreSQL: pgsql/doc/src/sgml/ref/alter_table.sgml,v 1.88 2006/08/03 20:57:06 tgl Exp $
 PostgreSQL documentation
 -->
 
@@ -741,6 +741,19 @@ ALTER TABLE foo
 </programlisting>
   </para>
 
+  <para>
+   The same, when the column has a default expression that won't automatically
+   cast to the new datatype:
+<programlisting>
+ALTER TABLE foo
+    ALTER COLUMN foo_timestamp DROP DEFAULT,
+    ALTER COLUMN foo_timestamp TYPE timestamp with time zone
+    USING
+        timestamp with time zone 'epoch' + foo_timestamp * interval '1 second',
+    ALTER COLUMN foo_timestamp SET DEFAULT now();
+</programlisting>
+  </para>
+
   <para>
    To rename an existing column:
 <programlisting>
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 3b408b411a..cd4c4eb230 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.198 2006/07/31 20:09:00 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.199 2006/08/03 20:57:06 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -2000,7 +2000,7 @@ ATPrepCmd(List **wqueue, Relation rel, AlterTableCmd *cmd,
 			ATSimplePermissions(rel, true);
 			ATSimpleRecursion(wqueue, rel, cmd, recurse);
 			/* No command-specific prep needed */
-			pass = AT_PASS_ADD_CONSTR;
+			pass = cmd->def ? AT_PASS_ADD_CONSTR : AT_PASS_DROP;
 			break;
 		case AT_DropNotNull:	/* ALTER COLUMN DROP NOT NULL */
 			ATSimplePermissions(rel, false);