Allow CHECK constraints to be declared ONLY

This makes them enforceable only on the parent table, not on children
tables.  This is useful in various situations, per discussion involving
people bitten by the restrictive behavior introduced in 8.4.

Message-Id:
8762mp93iw.fsf@comcast.net
CAFaPBrSMMpubkGf4zcRL_YL-AERUbYF_-ZNNYfb3CVwwEqc9TQ@mail.gmail.com

Authors: Nikhil Sontakke, Alex Hunsaker
Reviewed by Robert Haas and myself

1 files changed, 35 insertions, 15 deletions

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 135736a8dc6..00b6cb9d50d 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -579,6 +579,7 @@ DefineRelation(CreateStmt *stmt, char relkind, Oid ownerId)
 			cooked->skip_validation = false;
 			cooked->is_local = true;	/* not used for defaults */
 			cooked->inhcount = 0;		/* ditto */
+			cooked->is_only = false;
 			cookedDefaults = lappend(cookedDefaults, cooked);
 			descriptor->attrs[attnum - 1]->atthasdef = true;
 		}
@@ -638,7 +639,7 @@ DefineRelation(CreateStmt *stmt, char relkind, Oid ownerId)
 	 */
 	if (rawDefaults || stmt->constraints)
 		AddRelationNewConstraints(rel, rawDefaults, stmt->constraints,
-								  true, true);
+								  true, true, false);
 
 	/*
 	 * Clean up.  We keep lock on new relation (although it shouldn't be
@@ -1599,6 +1600,10 @@ MergeAttributes(List *schema, List *supers, char relpersistence,
 				char	   *name = check[i].ccname;
 				Node	   *expr;
 
+				/* ignore if the constraint is non-inheritable */
+				if (check[i].cconly)
+					continue;
+
 				/* adjust varattnos of ccbin here */
 				expr = stringToNode(check[i].ccbin);
 				change_varattnos_of_a_node(expr, newattno);
@@ -1617,6 +1622,7 @@ MergeAttributes(List *schema, List *supers, char relpersistence,
 					cooked->skip_validation = false;
 					cooked->is_local = false;
 					cooked->inhcount = 1;
+					cooked->is_only = false;
 					constraints = lappend(constraints, cooked);
 				}
 			}
@@ -4501,7 +4507,7 @@ ATExecAddColumn(List **wqueue, AlteredTableInfo *tab, Relation rel,
 		 * This function is intended for CREATE TABLE, so it processes a
 		 * _list_ of defaults, but we just do one.
 		 */
-		AddRelationNewConstraints(rel, list_make1(rawEnt), NIL, false, true);
+		AddRelationNewConstraints(rel, list_make1(rawEnt), NIL, false, true, false);
 
 		/* Make the additional catalog changes visible */
 		CommandCounterIncrement();
@@ -4898,7 +4904,7 @@ ATExecColumnDefault(Relation rel, const char *colName,
 		 * This function is intended for CREATE TABLE, so it processes a
 		 * _list_ of defaults, but we just do one.
 		 */
-		AddRelationNewConstraints(rel, list_make1(rawEnt), NIL, false, true);
+		AddRelationNewConstraints(rel, list_make1(rawEnt), NIL, false, true, false);
 	}
 }
 
@@ -5562,10 +5568,16 @@ ATAddCheckConstraint(List **wqueue, AlteredTableInfo *tab, Relation rel,
 	 * omitted from the returned list, which is what we want: we do not need
 	 * to do any validation work.  That can only happen at child tables,
 	 * though, since we disallow merging at the top level.
+	 *
+	 * Note: we set is_only based on the recurse flag which is false when
+	 * interpretInhOption() of our statement returns false all the way up
+	 * in AlterTable and gets passed all the way down to here.
 	 */
 	newcons = AddRelationNewConstraints(rel, NIL,
 										list_make1(copyObject(constr)),
-										recursing, !recursing);
+										recursing, /* allow_merge */
+										!recursing, /* is_local */
+										!recurse && !recursing); /* is_only */
 
 	/* Add each to-be-validated constraint to Phase 3's queue */
 	foreach(lcon, newcons)
@@ -5606,21 +5618,18 @@ ATAddCheckConstraint(List **wqueue, AlteredTableInfo *tab, Relation rel,
 		return;
 
 	/*
+	 * Adding an ONLY constraint? No need to find our children
+	 */
+	if (!recurse && !recursing)
+		return;
+
+	/*
 	 * 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.
 	 */
 	children = find_inheritance_children(RelationGetRelid(rel), lockmode);
 
-	/*
-	 * If we are told not to recurse, there had better not be any child
-	 * tables; else the addition would put them out of step.
-	 */
-	if (children && !recurse)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-				 errmsg("constraint must be added to child tables too")));
-
 	foreach(child, children)
 	{
 		Oid			childrelid = lfirst_oid(child);
@@ -5914,7 +5923,8 @@ ATAddForeignKeyConstraint(AlteredTableInfo *tab, Relation rel,
 									  NULL,
 									  NULL,
 									  true,		/* islocal */
-									  0);		/* inhcount */
+									  0,		/* inhcount */
+									  false);	/* isonly */
 
 	/*
 	 * Create the triggers that will enforce the constraint.
@@ -6755,6 +6765,7 @@ ATExecDropConstraint(Relation rel, const char *constrName,
 	HeapTuple	tuple;
 	bool		found = false;
 	bool		is_check_constraint = false;
+	bool		is_only_constraint = false;
 
 	/* At top level, permission check was done in ATPrepCmd, else do it */
 	if (recursing)
@@ -6791,6 +6802,12 @@ ATExecDropConstraint(Relation rel, const char *constrName,
 		/* Right now only CHECK constraints can be inherited */
 		if (con->contype == CONSTRAINT_CHECK)
 			is_check_constraint = true;
+		
+		if (con->conisonly)
+		{
+			Assert(is_check_constraint);
+			is_only_constraint = true;
+		}
 
 		/*
 		 * Perform the actual constraint deletion
@@ -6802,6 +6819,9 @@ ATExecDropConstraint(Relation rel, const char *constrName,
 		performDeletion(&conobj, behavior);
 
 		found = true;
+
+		/* constraint found and dropped -- no need to keep looping */
+		break;
 	}
 
 	systable_endscan(scan);
@@ -6830,7 +6850,7 @@ ATExecDropConstraint(Relation rel, const char *constrName,
 	 * 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.
 	 */
-	if (is_check_constraint)
+	if (is_check_constraint && !is_only_constraint)
 		children = find_inheritance_children(RelationGetRelid(rel), lockmode);
 	else
 		children = NIL;