1 files changed, 80 insertions, 83 deletions

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index fc3fc9b3846..80faae985e9 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -7899,6 +7899,7 @@ ATExecDropExpression(Relation rel, const char *colName, bool missing_ok, LOCKMOD
 	Form_pg_attribute attTup;
 	AttrNumber	attnum;
 	Relation	attrelation;
+	Oid			attrdefoid;
 	ObjectAddress address;
 
 	attrelation = table_open(AttributeRelationId, RowExclusiveLock);
@@ -7936,71 +7937,44 @@ ATExecDropExpression(Relation rel, const char *colName, bool missing_ok, LOCKMOD
 		}
 	}
 
+	/*
+	 * Mark the column as no longer generated.  (The atthasdef flag needs to
+	 * get cleared too, but RemoveAttrDefault will handle that.)
+	 */
 	attTup->attgenerated = '\0';
 	CatalogTupleUpdate(attrelation, &tuple->t_self, tuple);
 
 	InvokeObjectPostAlterHook(RelationRelationId,
 							  RelationGetRelid(rel),
-							  attTup->attnum);
-	ObjectAddressSubSet(address, RelationRelationId,
-						RelationGetRelid(rel), attnum);
+							  attnum);
 	heap_freetuple(tuple);
 
 	table_close(attrelation, RowExclusiveLock);
 
-	CommandCounterIncrement();
-
-	RemoveAttrDefault(RelationGetRelid(rel), attnum, DROP_RESTRICT, false, false);
-
 	/*
-	 * Remove all dependencies of this (formerly generated) column on other
-	 * columns in the same table.  (See StoreAttrDefault() for which
-	 * dependencies are created.)  We don't expect there to be dependencies
-	 * between columns of the same table for other reasons, so it's okay to
-	 * remove all of them.
+	 * Drop the dependency records of the GENERATED expression, in particular
+	 * its INTERNAL dependency on the column, which would otherwise cause
+	 * dependency.c to refuse to perform the deletion.
 	 */
-	{
-		Relation	depRel;
-		ScanKeyData key[3];
-		SysScanDesc scan;
-		HeapTuple	tup;
-
-		depRel = table_open(DependRelationId, RowExclusiveLock);
-
-		ScanKeyInit(&key[0],
-					Anum_pg_depend_classid,
-					BTEqualStrategyNumber, F_OIDEQ,
-					ObjectIdGetDatum(RelationRelationId));
-		ScanKeyInit(&key[1],
-					Anum_pg_depend_objid,
-					BTEqualStrategyNumber, F_OIDEQ,
-					ObjectIdGetDatum(RelationGetRelid(rel)));
-		ScanKeyInit(&key[2],
-					Anum_pg_depend_objsubid,
-					BTEqualStrategyNumber, F_INT4EQ,
-					Int32GetDatum(attnum));
+	attrdefoid = GetAttrDefaultOid(RelationGetRelid(rel), attnum);
+	if (!OidIsValid(attrdefoid))
+		elog(ERROR, "could not find attrdef tuple for relation %u attnum %d",
+			 RelationGetRelid(rel), attnum);
+	(void) deleteDependencyRecordsFor(AttrDefaultRelationId, attrdefoid, false);
 
-		scan = systable_beginscan(depRel, DependDependerIndexId, true,
-								  NULL, 3, key);
-
-		while (HeapTupleIsValid(tup = systable_getnext(scan)))
-		{
-			Form_pg_depend depform = (Form_pg_depend) GETSTRUCT(tup);
-
-			if (depform->refclassid == RelationRelationId &&
-				depform->refobjid == RelationGetRelid(rel) &&
-				depform->refobjsubid != 0 &&
-				depform->deptype == DEPENDENCY_AUTO)
-			{
-				CatalogTupleDelete(depRel, &tup->t_self);
-			}
-		}
-
-		systable_endscan(scan);
+	/* Make above changes visible */
+	CommandCounterIncrement();
 
-		table_close(depRel, RowExclusiveLock);
-	}
+	/*
+	 * Get rid of the GENERATED expression itself.  We use RESTRICT here for
+	 * safety, but at present we do not expect anything to depend on the
+	 * default.
+	 */
+	RemoveAttrDefault(RelationGetRelid(rel), attnum, DROP_RESTRICT,
+					  false, false);
 
+	ObjectAddressSubSet(address, RelationRelationId,
+						RelationGetRelid(rel), attnum);
 	return address;
 }
 
@@ -12548,21 +12522,6 @@ ATExecAlterColumnType(AlteredTableInfo *tab, Relation rel,
 						 */
 						Assert(foundObject.objectSubId == 0);
 					}
-					else if (relKind == RELKIND_RELATION &&
-							 foundObject.objectSubId != 0 &&
-							 get_attgenerated(foundObject.objectId, foundObject.objectSubId))
-					{
-						/*
-						 * Changing the type of a column that is used by a
-						 * generated column is not allowed by SQL standard. It
-						 * might be doable with some thinking and effort.
-						 */
-						ereport(ERROR,
-								(errcode(ERRCODE_SYNTAX_ERROR),
-								 errmsg("cannot alter type of a column used by a generated column"),
-								 errdetail("Column \"%s\" is used by generated column \"%s\".",
-										   colName, get_attname(foundObject.objectId, foundObject.objectSubId, false))));
-					}
 					else
 					{
 						/* Not expecting any other direct dependencies... */
@@ -12625,13 +12584,39 @@ ATExecAlterColumnType(AlteredTableInfo *tab, Relation rel,
 				break;
 
 			case OCLASS_DEFAULT:
+				{
+					ObjectAddress col = GetAttrDefaultColumnAddress(foundObject.objectId);
 
-				/*
-				 * Ignore the column's default expression, since we will fix
-				 * it below.
-				 */
-				Assert(defaultexpr);
-				break;
+					if (col.objectId == RelationGetRelid(rel) &&
+						col.objectSubId == attnum)
+					{
+						/*
+						 * Ignore the column's own default expression, which
+						 * we will deal with below.
+						 */
+						Assert(defaultexpr);
+					}
+					else
+					{
+						/*
+						 * This must be a reference from the expression of a
+						 * generated column elsewhere in the same table.
+						 * Changing the type of a column that is used by a
+						 * generated column is not allowed by SQL standard, so
+						 * just punt for now.  It might be doable with some
+						 * thinking and effort.
+						 */
+						ereport(ERROR,
+								(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+								 errmsg("cannot alter type of a column used by a generated column"),
+								 errdetail("Column \"%s\" is used by generated column \"%s\".",
+										   colName,
+										   get_attname(col.objectId,
+													   col.objectSubId,
+													   false))));
+					}
+					break;
+				}
 
 			case OCLASS_STATISTIC_EXT:
 
@@ -12694,9 +12679,8 @@ ATExecAlterColumnType(AlteredTableInfo *tab, Relation rel,
 
 	/*
 	 * Now scan for dependencies of this column on other things.  The only
-	 * thing we should find is the dependency on the column datatype, which we
-	 * want to remove, possibly a collation dependency, and dependencies on
-	 * other columns if it is a generated column.
+	 * things we should find are the dependency on the column datatype and
+	 * possibly a collation dependency.  Those can be removed.
 	 */
 	ScanKeyInit(&key[0],
 				Anum_pg_depend_classid,
@@ -12723,18 +12707,13 @@ ATExecAlterColumnType(AlteredTableInfo *tab, Relation rel,
 		foundObject.objectId = foundDep->refobjid;
 		foundObject.objectSubId = foundDep->refobjsubid;
 
-		if (foundDep->deptype != DEPENDENCY_NORMAL &&
-			foundDep->deptype != DEPENDENCY_AUTO)
+		if (foundDep->deptype != DEPENDENCY_NORMAL)
 			elog(ERROR, "found unexpected dependency type '%c'",
 				 foundDep->deptype);
 		if (!(foundDep->refclassid == TypeRelationId &&
 			  foundDep->refobjid == attTup->atttypid) &&
 			!(foundDep->refclassid == CollationRelationId &&
-			  foundDep->refobjid == attTup->attcollation) &&
-			!(foundDep->refclassid == RelationRelationId &&
-			  foundDep->refobjid == RelationGetRelid(rel) &&
-			  foundDep->refobjsubid != 0)
-			)
+			  foundDep->refobjid == attTup->attcollation))
 			elog(ERROR, "found unexpected dependency for column: %s",
 				 getObjectDescription(&foundObject, false));
 
@@ -12850,7 +12829,25 @@ ATExecAlterColumnType(AlteredTableInfo *tab, Relation rel,
 	 */
 	if (defaultexpr)
 	{
-		/* Must make new row visible since it will be updated again */
+		/*
+		 * If it's a GENERATED default, drop its dependency records, in
+		 * particular its INTERNAL dependency on the column, which would
+		 * otherwise cause dependency.c to refuse to perform the deletion.
+		 */
+		if (attTup->attgenerated)
+		{
+			Oid			attrdefoid = GetAttrDefaultOid(RelationGetRelid(rel), attnum);
+
+			if (!OidIsValid(attrdefoid))
+				elog(ERROR, "could not find attrdef tuple for relation %u attnum %d",
+					 RelationGetRelid(rel), attnum);
+			(void) deleteDependencyRecordsFor(AttrDefaultRelationId, attrdefoid, false);
+		}
+
+		/*
+		 * Make updates-so-far visible, particularly the new pg_attribute row
+		 * which will be updated again.
+		 */
 		CommandCounterIncrement();
 
 		/*