Remove hash-pruning logic for NULL values

It turns out some tests exercised this behavior, but removing it should
have no ill effects. Besides, both copy and INSERT disallow NULLs in a
table's partition column.

Fixes a bug where anti-joins on hash-partitioned distributed tables
would incorrectly prune shards early, result in incorrect results (test
included).

src/backend/distributed/planner/multi_physical_planner.c

@@ -134,7 +134,6 @@ static Node * HashableClauseMutator(Node *originalNode, Var *partitionColumn);
 static Var * MakeInt4Column(void);
 static Const * MakeInt4Constant(Datum constantValue);
 static OpExpr * MakeHashedOperatorExpression(OpExpr *operatorExpression);
-static OpExpr * MakeOpExpressionWithZeroConst(void);
 static List * BuildRestrictInfoList(List *qualList);
 static List * FragmentCombinationList(List *rangeTableFragmentsList, Query *jobQuery,
 									  List *dependedJobList);
@@ -2838,24 +2837,6 @@ HashableClauseMutator(Node *originalNode, Var *partitionColumn)
 			newNode = (Node *) hashedOperatorExpression;
 		}
 	}
-	else if (IsA(originalNode, NullTest))
-	{
-		NullTest *nullTest = (NullTest *) originalNode;
-		Var *column = NULL;
-
-		Expr *nullTestOperand = nullTest->arg;
-		if (IsA(nullTestOperand, Var))
-		{
-			column = (Var *) nullTestOperand;
-		}
-
-		if ((column != NULL) && equal(column, partitionColumn) &&
-			(nullTest->nulltesttype == IS_NULL))
-		{
-			OpExpr *opExpressionWithZeroConst = MakeOpExpressionWithZeroConst();
-			newNode = (Node *) opExpressionWithZeroConst;
-		}
-	}
 	else if (IsA(originalNode, ScalarArrayOpExpr))
 	{
 		ScalarArrayOpExpr *arrayOperatorExpression = (ScalarArrayOpExpr *) originalNode;
@@ -3034,23 +3015,6 @@ MakeInt4Constant(Datum constantValue)
 }
 
 
-/*
- * MakeOpExpressionWithZeroConst creates a new operator expression with equality
- * check to zero and returns it.
- */
-static OpExpr *
-MakeOpExpressionWithZeroConst()
-{
-	Var *int4Column = MakeInt4Column();
-	OpExpr *operatorExpression = MakeOpExpression(int4Column, BTEqualStrategyNumber);
-	Const *constant = (Const *) get_rightop((Expr *) operatorExpression);
-	constant->constvalue = Int32GetDatum(0);
-	constant->constisnull = false;
-
-	return operatorExpression;
-}
-
-
 /*
  * BuildRestrictInfoList builds restrict info list using the selection criteria,
  * and then return this list. Note that this function assumes there is only one

src/test/regress/expected/multi_hash_pruning.out

@@ -178,9 +178,6 @@ DEBUG:  predicate pruning for shardId 630003
 
 SET citus.task_executor_type TO :actual_task_executor;
 SELECT count(*) FROM orders_hash_partitioned WHERE o_orderkey is NULL;
-DEBUG:  predicate pruning for shardId 630000
-DEBUG:  predicate pruning for shardId 630001
-DEBUG:  predicate pruning for shardId 630003
  count 
 -------
      0
@@ -225,8 +222,6 @@ DEBUG:  predicate pruning for shardId 630003
 
 SELECT count(*) FROM orders_hash_partitioned
 	WHERE o_orderkey = 1 OR o_orderkey is NULL;
-DEBUG:  predicate pruning for shardId 630001
-DEBUG:  predicate pruning for shardId 630003
  count 
 -------
      0
@@ -324,12 +319,11 @@ SELECT count(*)
 DEBUG:  predicate pruning for shardId 630001
 DEBUG:  predicate pruning for shardId 630002
 DEBUG:  predicate pruning for shardId 630003
-DEBUG:  predicate pruning for shardId 630000
-DEBUG:  predicate pruning for shardId 630001
-DEBUG:  predicate pruning for shardId 630003
+DEBUG:  join prunable for intervals [-2147483648,-1073741825] and [-1073741824,-1]
 DEBUG:  join prunable for intervals [-2147483648,-1073741825] and [0,1073741823]
+DEBUG:  join prunable for intervals [-2147483648,-1073741825] and [1073741824,2147483647]
  count 
 -------
-      
+     0
 (1 row)
 

src/test/regress/expected/multi_prune_shard_list.out

@@ -59,11 +59,11 @@ SELECT prune_using_single_value('pruning', 'tomato');
  {800002}
 (1 row)
 
--- the above is true even if that value is null
+-- null values should result in no pruning
 SELECT prune_using_single_value('pruning', NULL);
- prune_using_single_value 
---------------------------
- {800002}
+   prune_using_single_value    
+-------------------------------
+ {800000,800001,800002,800003}
 (1 row)
 
 -- build an OR clause and expect more than one sahrd

src/test/regress/input/multi_outer_join.source

@@ -415,3 +415,36 @@ FROM
 	LEFT OUTER JOIN multi_outer_join_left l1 ON (l1.l_custkey = r1.r_custkey)) AS
     test(c_custkey, c_nationkey)
     INNER JOIN multi_outer_join_third t1 ON (test.c_custkey = t1.t_custkey);
+
+-- simple test to ensure anti-joins work with hash-partitioned tables
+CREATE TABLE left_values(val int);
+
+SELECT master_create_distributed_table('left_values', 'val', 'hash');
+SELECT master_create_worker_shards('left_values', 16, 1);
+
+\copy left_values from stdin
+1
+2
+3
+4
+5
+\.
+
+CREATE TABLE right_values(val int);
+
+SELECT master_create_distributed_table('right_values', 'val', 'hash');
+SELECT master_create_worker_shards('right_values', 16, 1);
+
+\copy right_values from stdin
+2
+3
+4
+\.
+
+SELECT
+    *
+FROM
+    left_values AS l
+    LEFT JOIN right_values AS r ON l.val = r.val
+WHERE
+    r.val IS NULL;

src/test/regress/output/multi_outer_join.source

@@ -762,3 +762,46 @@ FROM
     INNER JOIN multi_outer_join_third t1 ON (test.c_custkey = t1.t_custkey);
 ERROR:  cannot perform distributed planning on this query
 DETAIL:  Shards of relations in outer join queries must have 1-to-1 shard partitioning
+-- simple test to ensure anti-joins work with hash-partitioned tables
+CREATE TABLE left_values(val int);
+SELECT master_create_distributed_table('left_values', 'val', 'hash');
+ master_create_distributed_table 
+---------------------------------
+ 
+(1 row)
+
+SELECT master_create_worker_shards('left_values', 16, 1);
+ master_create_worker_shards 
+-----------------------------
+ 
+(1 row)
+
+\copy left_values from stdin
+CREATE TABLE right_values(val int);
+SELECT master_create_distributed_table('right_values', 'val', 'hash');
+ master_create_distributed_table 
+---------------------------------
+ 
+(1 row)
+
+SELECT master_create_worker_shards('right_values', 16, 1);
+ master_create_worker_shards 
+-----------------------------
+ 
+(1 row)
+
+\copy right_values from stdin
+SELECT
+    *
+FROM
+    left_values AS l
+    LEFT JOIN right_values AS r ON l.val = r.val
+WHERE
+    r.val IS NULL;
+LOG:  join order: [ "left_values" ][ local partition join "right_values" ]
+ val | val 
+-----+-----
+   1 |    
+   5 |    
+(2 rows)
+

src/test/regress/sql/multi_prune_shard_list.sql

@@ -54,7 +54,7 @@ SELECT prune_using_no_values('pruning');
 -- with a single value, expect a single shard
 SELECT prune_using_single_value('pruning', 'tomato');
 
--- the above is true even if that value is null
+-- null values should result in no pruning
 SELECT prune_using_single_value('pruning', NULL);
 
 -- build an OR clause and expect more than one sahrd