Merge pull request #1918 from citusdata/fix_outer_join_pushdown

Outer joins should also use/try subquery pushdown planner if join clause is not supported

src/backend/distributed/planner/multi_logical_planner.c

@@ -224,7 +224,7 @@ MultiLogicalPlanCreate(Query *originalQuery, Query *queryTree,
 static bool
 ShouldUseSubqueryPushDown(Query *originalQuery, Query *rewrittenQuery)
 {
-	List *whereClauseList = NIL;
+	List *qualifierList = NIL;
 
 	/*
 	 * We check the existence of subqueries in FROM clause on the modified query
@@ -260,8 +260,8 @@ ShouldUseSubqueryPushDown(Query *originalQuery, Query *rewrittenQuery)
 	 * Some unsupported join clauses in logical planner
 	 * may be supported by subquery pushdown planner.
 	 */
-	whereClauseList = WhereClauseList(rewrittenQuery->jointree);
+	qualifierList = QualifierList(rewrittenQuery->jointree);
-	if (DeferErrorIfUnsupportedClause(whereClauseList) != NULL)
+	if (DeferErrorIfUnsupportedClause(qualifierList) != NULL)
 	{
 		return true;
 	}

src/test/regress/expected/multi_subquery.out

@@ -390,6 +390,99 @@ WHERE
 ORDER BY l_orderkey DESC
 LIMIT 10;
 ERROR:  complex joins are only supported when all distributed tables are joined on their distribution columns with equal operator
+-- outer joins on reference tables with functions works
+SELECT DISTINCT ON (t1.user_id) t1.user_id, t2.value_1, t2.value_2, t2.value_3
+FROM events_table t1
+LEFT JOIN users_reference_table t2 ON t1.user_id = trunc(t2.user_id)
+ORDER BY 1 DESC, 2 DESC, 3 DESC, 4 DESC 
+LIMIT 5;
+ user_id | value_1 | value_2 | value_3 
+---------+---------+---------+---------
+       6 |       5 |       2 |       0
+       5 |       5 |       5 |       1
+       4 |       5 |       4 |       1
+       3 |       5 |       5 |       3
+       2 |       4 |       4 |       5
+(5 rows)
+
+-- outer joins on reference tables with simple expressions should work
+SELECT DISTINCT ON (t1.user_id) t1.user_id, t2.value_1, t2.value_2, t2.value_3
+FROM events_table t1
+LEFT JOIN users_reference_table t2 ON t1.user_id > t2.user_id
+ORDER BY 1 DESC, 2 DESC, 3 DESC, 4 DESC 
+LIMIT 5;
+ user_id | value_1 | value_2 | value_3 
+---------+---------+---------+---------
+       6 |       5 |       5 |       3
+       5 |       5 |       5 |       3
+       4 |       5 |       5 |       3
+       3 |       5 |       4 |       3
+       2 |       5 |       4 |       3
+(5 rows)
+
+-- outer joins on distributed tables with simple expressions should not work
+SELECT DISTINCT ON (t1.user_id) t1.user_id, t2.value_1, t2.value_2, t2.value_3
+FROM events_table t1
+LEFT JOIN users_table t2 ON t1.user_id > t2.user_id
+ORDER BY 1 DESC, 2 DESC, 3 DESC, 4 DESC 
+LIMIT 5;
+ERROR:  complex joins are only supported when all distributed tables are joined on their distribution columns with equal operator
+-- outer joins on reference tables with expressions should work
+SELECT DISTINCT ON (t1.user_id) t1.user_id, t2.value_1, t2.value_2, t2.value_3
+FROM events_table t1
+LEFT JOIN users_reference_table t2 ON t1.user_id = (CASE WHEN t2.user_id > 3 THEN 3 ELSE t2.user_id END)
+ORDER BY 1 DESC, 2 DESC, 3 DESC, 4 DESC 
+LIMIT 5;
+ user_id | value_1 | value_2 | value_3 
+---------+---------+---------+---------
+       6 |         |         |        
+       5 |         |         |        
+       4 |         |         |        
+       3 |       5 |       5 |       3
+       2 |       4 |       4 |       5
+(5 rows)
+
+-- outer joins on distributed tables and reference tables with expressions should work
+SELECT DISTINCT ON (t1.user_id) t1.user_id, t2.value_1, t2.value_2, t2.value_3
+ FROM 
+ users_table t0 LEFT JOIN
+ events_table t1  ON t0.user_id = t1.user_id
+ LEFT JOIN users_reference_table t2 ON t1.user_id = trunc(t2.user_id)
+ ORDER BY 1 DESC, 2 DESC, 3 DESC, 4 DESC 
+ LIMIT 5;
+ user_id | value_1 | value_2 | value_3 
+---------+---------+---------+---------
+       6 |       5 |       2 |       0
+       5 |       5 |       5 |       1
+       4 |       5 |       4 |       1
+       3 |       5 |       5 |       3
+       2 |       4 |       4 |       5
+(5 rows)
+
+-- outer joins on distributed tables with expressions should not work
+SELECT DISTINCT ON (t1.user_id) t1.user_id, t2.value_1, t2.value_2, t2.value_3
+ FROM 
+ users_table t0 LEFT JOIN
+ events_table t1  ON t0.user_id = trunc(t1.user_id)
+ LEFT JOIN users_reference_table t2 ON t1.user_id = trunc(t2.user_id)
+ ORDER BY 1 DESC, 2 DESC, 3 DESC, 4 DESC 
+ LIMIT 5;
+ERROR:  complex joins are only supported when all distributed tables are joined on their distribution columns with equal operator
+-- inner joins on reference tables with functions works
+SELECT DISTINCT ON (t1.user_id) t1.user_id, t2.value_1, t2.value_2, t2.value_3
+FROM events_table t1
+JOIN users_reference_table t2 ON t1.user_id = trunc(t2.user_id)
+ORDER BY 1 DESC, 2 DESC, 3 DESC, 4 DESC 
+LIMIT 5;
+ user_id | value_1 | value_2 | value_3 
+---------+---------+---------+---------
+       6 |       5 |       2 |       0
+       5 |       5 |       5 |       1
+       4 |       5 |       4 |       1
+       3 |       5 |       5 |       3
+       2 |       4 |       4 |       5
+(5 rows)
+
 -- distinct queries work
 SELECT DISTINCT l_orderkey
 FROM

src/test/regress/sql/multi_subquery.sql

@@ -279,6 +279,59 @@ WHERE
 ORDER BY l_orderkey DESC
 LIMIT 10;
 
+-- outer joins on reference tables with functions works
+SELECT DISTINCT ON (t1.user_id) t1.user_id, t2.value_1, t2.value_2, t2.value_3
+FROM events_table t1
+LEFT JOIN users_reference_table t2 ON t1.user_id = trunc(t2.user_id)
+ORDER BY 1 DESC, 2 DESC, 3 DESC, 4 DESC 
+LIMIT 5;
+
+-- outer joins on reference tables with simple expressions should work
+SELECT DISTINCT ON (t1.user_id) t1.user_id, t2.value_1, t2.value_2, t2.value_3
+FROM events_table t1
+LEFT JOIN users_reference_table t2 ON t1.user_id > t2.user_id
+ORDER BY 1 DESC, 2 DESC, 3 DESC, 4 DESC 
+LIMIT 5;
+
+-- outer joins on distributed tables with simple expressions should not work
+SELECT DISTINCT ON (t1.user_id) t1.user_id, t2.value_1, t2.value_2, t2.value_3
+FROM events_table t1
+LEFT JOIN users_table t2 ON t1.user_id > t2.user_id
+ORDER BY 1 DESC, 2 DESC, 3 DESC, 4 DESC 
+LIMIT 5;
+
+-- outer joins on reference tables with expressions should work
+SELECT DISTINCT ON (t1.user_id) t1.user_id, t2.value_1, t2.value_2, t2.value_3
+FROM events_table t1
+LEFT JOIN users_reference_table t2 ON t1.user_id = (CASE WHEN t2.user_id > 3 THEN 3 ELSE t2.user_id END)
+ORDER BY 1 DESC, 2 DESC, 3 DESC, 4 DESC 
+LIMIT 5;
+
+-- outer joins on distributed tables and reference tables with expressions should work
+SELECT DISTINCT ON (t1.user_id) t1.user_id, t2.value_1, t2.value_2, t2.value_3
+ FROM 
+ users_table t0 LEFT JOIN
+ events_table t1  ON t0.user_id = t1.user_id
+ LEFT JOIN users_reference_table t2 ON t1.user_id = trunc(t2.user_id)
+ ORDER BY 1 DESC, 2 DESC, 3 DESC, 4 DESC 
+ LIMIT 5;
+
+-- outer joins on distributed tables with expressions should not work
+SELECT DISTINCT ON (t1.user_id) t1.user_id, t2.value_1, t2.value_2, t2.value_3
+ FROM 
+ users_table t0 LEFT JOIN
+ events_table t1  ON t0.user_id = trunc(t1.user_id)
+ LEFT JOIN users_reference_table t2 ON t1.user_id = trunc(t2.user_id)
+ ORDER BY 1 DESC, 2 DESC, 3 DESC, 4 DESC 
+ LIMIT 5;
+
+-- inner joins on reference tables with functions works
+SELECT DISTINCT ON (t1.user_id) t1.user_id, t2.value_1, t2.value_2, t2.value_3
+FROM events_table t1
+JOIN users_reference_table t2 ON t1.user_id = trunc(t2.user_id)
+ORDER BY 1 DESC, 2 DESC, 3 DESC, 4 DESC 
+LIMIT 5;
+
 -- distinct queries work
 SELECT DISTINCT l_orderkey
 FROM