Don't disallow DROP of constraints ONLY on partitioned tables

This restriction seems to have come about due to some fuzzy thinking: in
commit 9139aa19423b we were adding a restriction against ADD constraint
ONLY on partitioned tables (which is sensible) and apparently we thought
the DROP case had to be symmetrical.  However, it isn't, and the
comments about it are mistaken about the effect it would have.  Remove
this limitation.

There have been no reports of users bothered by this limitation, so I'm
not backpatching it just yet.  We can revisit this decision later, as needed.

Reviewed-by: Amit Langote <amitlangote09@gmail.com>
Discussion: https://postgr.es/m/202409261752.nbvlawkxsttf@alvherre.pgsql
Discussion: https://postgr.es/m/7682253a-6f79-6a92-00aa-267c4c412870@lab.ntt.co.jp
	(about commit 9139aa19423b, previously not registered)

1 files changed, 1 insertions, 37 deletions

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 7405023e77b..96373323b8d 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -447,7 +447,6 @@ static bool check_for_column_name_collision(Relation rel, const char *colname,
 											bool if_not_exists);
 static void add_column_datatype_dependency(Oid relid, int32 attnum, Oid typid);
 static void add_column_collation_dependency(Oid relid, int32 attnum, Oid collid);
-static void ATPrepDropNotNull(Relation rel, bool recurse, bool recursing);
 static ObjectAddress ATExecDropNotNull(Relation rel, const char *colName, LOCKMODE lockmode);
 static void ATPrepSetNotNull(List **wqueue, Relation rel,
 							 AlterTableCmd *cmd, bool recurse, bool recursing,
@@ -4858,7 +4857,6 @@ ATPrepCmd(List **wqueue, Relation rel, AlterTableCmd *cmd,
 		case AT_DropNotNull:	/* ALTER COLUMN DROP NOT NULL */
 			ATSimplePermissions(cmd->subtype, rel,
 								ATT_TABLE | ATT_PARTITIONED_TABLE | ATT_FOREIGN_TABLE);
-			ATPrepDropNotNull(rel, recurse, recursing);
 			ATSimpleRecursion(wqueue, rel, cmd, recurse, lockmode, context);
 			pass = AT_PASS_DROP;
 			break;
@@ -7498,29 +7496,7 @@ add_column_collation_dependency(Oid relid, int32 attnum, Oid collid)
 
 /*
  * ALTER TABLE ALTER COLUMN DROP NOT NULL
- */
-
-static void
-ATPrepDropNotNull(Relation rel, bool recurse, bool recursing)
-{
-	/*
-	 * If the parent is a partitioned table, like check constraints, we do not
-	 * support removing the NOT NULL while partitions exist.
-	 */
-	if (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
-	{
-		PartitionDesc partdesc = RelationGetPartitionDesc(rel, true);
-
-		Assert(partdesc != NULL);
-		if (partdesc->nparts > 0 && !recurse && !recursing)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-					 errmsg("cannot remove constraint from only the partitioned table when partitions exist"),
-					 errhint("Do not specify the ONLY keyword.")));
-	}
-}
-
-/*
+ *
  * Return the address of the modified column.  If the column was already
  * nullable, InvalidObjectAddress is returned.
  */
@@ -12713,18 +12689,6 @@ ATExecDropConstraint(Relation rel, const char *constrName,
 	else
 		children = NIL;
 
-	/*
-	 * For a partitioned table, if partitions exist and we are told not to
-	 * recurse, it's a user error.  It doesn't make sense to have a constraint
-	 * be defined only on the parent, especially if it's a partitioned table.
-	 */
-	if (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE &&
-		children != NIL && !recurse)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-				 errmsg("cannot remove constraint from only the partitioned table when partitions exist"),
-				 errhint("Do not specify the ONLY keyword.")));
-
 	foreach_oid(childrelid, children)
 	{
 		Relation	childrel;