Allow ALTER TABLE ONLY on partitioned tables

There is no need to forbid ALTER TABLE ONLY on partitioned tables,
when no partitions exist yet.  This can be handy for users who are
building up their partitioned table independently and will create actual
partitions later.

In addition, this is how pg_dump likes to operate in certain instances.

Author: Amit Langote, with some error message word-smithing by me

1 files changed, 41 insertions, 25 deletions

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index a02904c85c9..a35713096d9 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -1259,7 +1259,8 @@ ExecuteTruncate(TruncateStmt *stmt)
 		else if (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
 			ereport(ERROR,
 					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-					 errmsg("must truncate child tables too")));
+					 errmsg("cannot truncate only a partitioned table"),
+					 errhint("Do not specify the ONLY keyword, or use truncate only on the partitions directly.")));
 	}
 
 	/*
@@ -5578,14 +5579,20 @@ static void
 ATPrepDropNotNull(Relation rel, bool recurse, bool recursing)
 {
 	/*
-	 * If the parent is a partitioned table, like check constraints, NOT NULL
-	 * constraints must be dropped from child tables.
+	 * 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 &&
-		!recurse && !recursing)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-				 errmsg("constraint must be dropped from child tables too")));
+	if (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
+	{
+		PartitionDesc	partdesc = RelationGetPartitionDesc(rel);
+
+		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.")));
+	}
 }
 static ObjectAddress
 ATExecDropNotNull(Relation rel, const char *colName, LOCKMODE lockmode)
@@ -5746,13 +5753,19 @@ ATPrepSetNotNull(Relation rel, bool recurse, bool recursing)
 {
 	/*
 	 * If the parent is a partitioned table, like check constraints, NOT NULL
-	 * constraints must be added to the child tables.
+	 * constraints must be added to the child tables.  Complain if requested
+	 * otherwise and partitions exist.
 	 */
-	if (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE &&
-		!recurse && !recursing)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-				 errmsg("constraint must be added to child tables too")));
+	if (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
+	{
+		PartitionDesc	partdesc = RelationGetPartitionDesc(rel);
+
+		if (partdesc && partdesc->nparts > 0 && !recurse && !recursing)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+					 errmsg("cannot add constraint to only the partitioned table when partitions exist"),
+					 errhint("Do not specify the ONLY keyword.")));
+	}
 }
 
 static ObjectAddress
@@ -6547,7 +6560,8 @@ ATExecDropColumn(List **wqueue, Relation rel, const char *colName,
 		if (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE && !recurse)
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-					 errmsg("column must be dropped from child tables too")));
+					 errmsg("cannot drop column from only the partitioned table when partitions exist"),
+					 errhint("Do not specify the ONLY keyword.")));
 
 		attr_rel = heap_open(AttributeRelationId, RowExclusiveLock);
 		foreach(child, children)
@@ -8562,16 +8576,6 @@ ATExecDropConstraint(Relation rel, const char *constrName,
 	}
 
 	/*
-	 * In case of a partitioned table, the constraint must be dropped from the
-	 * partitions too.  There is no such thing as NO INHERIT constraints in
-	 * case of partitioned tables.
-	 */
-	if (!recurse && rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-				 errmsg("constraint must be dropped from child tables too")));
-
-	/*
 	 * Propagate to children as appropriate.  Unlike most other ALTER
 	 * routines, we have to do this one level of recursion at a time; we can't
 	 * use find_all_inheritors to do it in one pass.
@@ -8581,6 +8585,18 @@ 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(child, children)
 	{
 		Oid			childrelid = lfirst_oid(child);