Fix code related to partitioning schemes for dropped columns.

The entry in appinfo->translated_vars can be NULL; if so, we must avoid
dereferencing it.

Ashutosh Bapat

Discussion: http://postgr.es/m/CAFjFpReL7+1ien=-21rhjpO3bV7aAm1rQ8XgLVk2csFagSzpZQ@mail.gmail.com

src/backend/optimizer/path/allpaths.c

@@ -950,6 +950,18 @@ set_append_rel_size(PlannerInfo *root, RelOptInfo *rel,
 													attno - 1);
 					int			child_index;
 
+					/*
+					 * Ignore any column dropped from the parent.
+					 * Corresponding Var won't have any translation. It won't
+					 * have attr_needed information, since it can not be
+					 * referenced in the query.
+					 */
+					if (var == NULL)
+					{
+						Assert(attr_needed == NULL);
+						continue;
+					}
+
 					child_index = var->varattno - childrel->min_attr;
 					childrel->attr_needed[child_index] = attr_needed;
 				}

src/test/regress/expected/alter_table.out

@@ -3706,6 +3706,13 @@ ALTER TABLE list_parted2 DROP COLUMN b;
 ERROR:  cannot drop column named in partition key
 ALTER TABLE list_parted2 ALTER COLUMN b TYPE text;
 ERROR:  cannot alter type of column named in partition key
+-- dropping non-partition key columns should be allowed on the parent table.
+ALTER TABLE list_parted DROP COLUMN b;
+SELECT * FROM list_parted;
+ a 
+---
+(0 rows)
+
 -- cleanup
 DROP TABLE list_parted, list_parted2, range_parted;
 DROP TABLE fail_def_part;

src/test/regress/sql/alter_table.sql

@@ -2418,6 +2418,10 @@ ALTER TABLE part_2 INHERIT inh_test;
 ALTER TABLE list_parted2 DROP COLUMN b;
 ALTER TABLE list_parted2 ALTER COLUMN b TYPE text;
 
+-- dropping non-partition key columns should be allowed on the parent table.
+ALTER TABLE list_parted DROP COLUMN b;
+SELECT * FROM list_parted;
+
 -- cleanup
 DROP TABLE list_parted, list_parted2, range_parted;
 DROP TABLE fail_def_part;