Fix not-null constraint test

When a partitioned table has a primary key, trying to find the
corresponding not-null constraint for that column would come up empty,
causing code that's trying to check said not-null constraint to crash.
Fix by only running the check when the not-null constraint exists.

Reported-by: Alexander Lakhin <exclusion@gmail.com>
Discussion: https://postgr.es/m/d57b4a69-7394-3146-5976-9a1ef27e7972@gmail.com

src/backend/commands/tablecmds.c

@@ -15746,9 +15746,10 @@ MergeAttributesIntoExisting(Relation child_rel, Relation parent_rel)
 								attributeName)));
 
 			/*
-			 * Check child doesn't discard NOT NULL property.  (Other
-			 * constraints are checked elsewhere.)  However, if the constraint
-			 * is NO INHERIT in the parent, this is allowed.
+			 * If the parent has a not-null constraint that's not NO INHERIT,
+			 * make sure the child has one too.
+			 *
+			 * Other constraints are checked elsewhere.
 			 */
 			if (attribute->attnotnull && !childatt->attnotnull)
 			{
@@ -15756,11 +15757,12 @@ MergeAttributesIntoExisting(Relation child_rel, Relation parent_rel)
 
 				contup = findNotNullConstraintAttnum(RelationGetRelid(parent_rel),
 													 attribute->attnum);
-				if (!((Form_pg_constraint) GETSTRUCT(contup))->connoinherit)
+				if (HeapTupleIsValid(contup) &&
+					!((Form_pg_constraint) GETSTRUCT(contup))->connoinherit)
 					ereport(ERROR,
-							(errcode(ERRCODE_DATATYPE_MISMATCH),
-							 errmsg("column \"%s\" in child table must be marked NOT NULL",
-									attributeName)));
+							errcode(ERRCODE_DATATYPE_MISMATCH),
+							errmsg("column \"%s\" in child table must be marked NOT NULL",
+								   attributeName));
 			}
 
 			/*
@@ -15981,10 +15983,20 @@ MergeConstraintsIntoExisting(Relation child_rel, Relation parent_rel)
 		systable_endscan(child_scan);
 
 		if (!found)
+		{
+			if (parent_con->contype == CONSTRAINT_NOTNULL)
+				ereport(ERROR,
+						errcode(ERRCODE_DATATYPE_MISMATCH),
+						errmsg("column \"%s\" in child table must be marked NOT NULL",
+							   get_attname(parent_relid,
+										   extractNotNullColumn(parent_tuple),
+										   false)));
+
 			ereport(ERROR,
 					(errcode(ERRCODE_DATATYPE_MISMATCH),
 					 errmsg("child table is missing constraint \"%s\"",
 							NameStr(parent_con->conname))));
+		}
 	}
 
 	systable_endscan(parent_scan);

src/test/regress/expected/constraints.out

@@ -1006,6 +1006,17 @@ Inherits: cnn_grandchild,
 ALTER TABLE cnn_parent DROP CONSTRAINT cnn_parent_pkey;
 ERROR:  constraint "cnn_parent_pkey" of relation "cnn_parent" does not exist
 -- keeps these tables around, for pg_upgrade testing
+-- ensure columns in partitions are marked not-null
+create table cnn2_parted(a int primary key) partition by list (a);
+create table cnn2_part1(a int);
+alter table cnn2_parted attach partition cnn2_part1 for values in (1);
+ERROR:  primary key column "a" is not marked NOT NULL
+drop table cnn2_parted, cnn2_part1;
+create table cnn2_parted(a int not null) partition by list (a);
+create table cnn2_part1(a int primary key);
+alter table cnn2_parted attach partition cnn2_part1 for values in (1);
+ERROR:  column "a" in child table must be marked NOT NULL
+drop table cnn2_parted, cnn2_part1;
 -- Comments
 -- Setup a low-level role to enforce non-superuser checks.
 CREATE ROLE regress_constraint_comments;

src/test/regress/sql/constraints.sql

@@ -657,6 +657,17 @@ ALTER TABLE cnn_parent ADD PRIMARY KEY USING INDEX b_uq;
 ALTER TABLE cnn_parent DROP CONSTRAINT cnn_parent_pkey;
 -- keeps these tables around, for pg_upgrade testing
 
+-- ensure columns in partitions are marked not-null
+create table cnn2_parted(a int primary key) partition by list (a);
+create table cnn2_part1(a int);
+alter table cnn2_parted attach partition cnn2_part1 for values in (1);
+drop table cnn2_parted, cnn2_part1;
+
+create table cnn2_parted(a int not null) partition by list (a);
+create table cnn2_part1(a int primary key);
+alter table cnn2_parted attach partition cnn2_part1 for values in (1);
+drop table cnn2_parted, cnn2_part1;
+
 
 -- Comments
 -- Setup a low-level role to enforce non-superuser checks.