unsupported subquery error messages are fixed

src/backend/distributed/planner/multi_logical_planner.c

@@ -960,14 +960,16 @@ DeferErrorIfCannotPushdownSubquery(Query *subqueryTree, bool outerMostQueryHasLi
 	if (subqueryTree->limitOffset)
 	{
 		preconditionsSatisfied = false;
-		errorDetail = "Offset clause is currently unsupported";
+		errorDetail = "Offset clause is currently unsupported when a subquery "
+					  "references a column from another query";
 	}
 
 	/* limit is not supported when SubqueryPushdown is not set */
 	if (subqueryTree->limitCount && !SubqueryPushdown)
 	{
 		preconditionsSatisfied = false;
-		errorDetail = "Limit in subquery is currently unsupported";
+		errorDetail = "Limit in subquery is currently unsupported when a "
+					  "subquery references a column from another query";
 	}
 
 	/*
@@ -1022,7 +1024,8 @@ DeferErrorIfCannotPushdownSubquery(Query *subqueryTree, bool outerMostQueryHasLi
 		{
 			preconditionsSatisfied = false;
 			errorDetail = "Group by list without partition column is currently "
-						  "unsupported";
+						  "unsupported when a subquery references a column "
+						  "from another query";
 		}
 	}
 
@@ -1041,7 +1044,8 @@ DeferErrorIfCannotPushdownSubquery(Query *subqueryTree, bool outerMostQueryHasLi
 	if (subqueryTree->hasAggs && (subqueryTree->groupClause == NULL))
 	{
 		preconditionsSatisfied = false;
-		errorDetail = "Aggregates without group by are currently unsupported";
+		errorDetail = "Aggregates without group by are currently unsupported "
+					  "when a subquery references a column from another query";
 	}
 
 	/* having clause without group by on partition column is not supported */
@@ -1049,7 +1053,8 @@ DeferErrorIfCannotPushdownSubquery(Query *subqueryTree, bool outerMostQueryHasLi
 	{
 		preconditionsSatisfied = false;
 		errorDetail = "Having qual without group by on partition column is "
-					  "currently unsupported";
+					  "currently unsupported when a subquery references "
+					  "a column from another query";
 	}
 
 	/* distinct clause list must include partition column */

src/test/regress/expected/multi_subquery_complex_queries.out

@@ -1213,7 +1213,7 @@ ORDER BY
   user_id
 limit 50;
 ERROR:  cannot push down this subquery
-DETAIL:  Limit in subquery is currently unsupported
+DETAIL:  Limit in subquery is currently unsupported when a subquery references a column from another query
 -- we recursively plan some queries but fail in the end 
 -- since some_users_data since it has a reference
 -- from an outer query which is not recursively planned
@@ -1250,7 +1250,7 @@ ORDER BY
   user_id
 limit 50;
 ERROR:  cannot push down this subquery
-DETAIL:  Limit in subquery is currently unsupported
+DETAIL:  Limit in subquery is currently unsupported when a subquery references a column from another query
 -- LATERAL JOINs used with INNER JOINs
 SET citus.subquery_pushdown to ON;
 SELECT user_id, lastseen
@@ -1598,7 +1598,7 @@ ORDER BY
   user_id DESC
 LIMIT 10;
 ERROR:  cannot push down this subquery
-DETAIL:  Limit in subquery is currently unsupported
+DETAIL:  Limit in subquery is currently unsupported when a subquery references a column from another query
 -- NESTED INNER JOINs
 SELECT 
  count(*) AS value, "generated_group_field" 
@@ -2200,7 +2200,7 @@ ORDER BY
     value_2 DESC, user_id DESC
 LIMIT 10;
 ERROR:  cannot push down this subquery
-DETAIL:  Limit in subquery is currently unsupported
+DETAIL:  Limit in subquery is currently unsupported when a subquery references a column from another query
 -- lets test some unsupported set operations
 -- not supported since we use INTERSECT
 SELECT ("final_query"."event_types") as types, count(*) AS sumOfEventType

src/test/regress/expected/multi_subquery_in_where_clause.out

@@ -610,7 +610,7 @@ WHERE
            OFFSET 3
           );
 ERROR:  cannot push down this subquery
-DETAIL:  Offset clause is currently unsupported
+DETAIL:  Offset clause is currently unsupported when a subquery references a column from another query
 -- we can detect unsupported subquerues even if they appear
 -- in WHERE subquery -> FROM subquery -> WHERE subquery
 -- but we can recursively plan that anyway

src/test/regress/expected/multi_subquery_in_where_reference_clause.out

@@ -493,7 +493,7 @@ HAVING count(*) > 3
 ORDER BY user_id
 LIMIT 5;
 ERROR:  cannot push down this subquery
-DETAIL:  Group by list without partition column is currently unsupported
+DETAIL:  Group by list without partition column is currently unsupported when a subquery references a column from another query
 -- similar query with slightly more complex group by
 -- though the error message is a bit confusing
 SELECT 
@@ -516,4 +516,4 @@ HAVING count(*) > 3
 ORDER BY user_id
 LIMIT 5;
 ERROR:  cannot push down this subquery
-DETAIL:  Group by list without partition column is currently unsupported
+DETAIL:  Group by list without partition column is currently unsupported when a subquery references a column from another query

src/test/regress/expected/subqueries_not_supported.out

@@ -143,6 +143,46 @@ DEBUG:  generating subplan 17_1 for subquery SELECT users_table.value_2 FROM pub
 DEBUG:  Plan 17 query after replacing subqueries and CTEs: SELECT foo.value_2 FROM ((SELECT intermediate_result.value_2 FROM read_intermediate_result('17_1'::text, 'binary'::citus_copy_format) intermediate_result(value_2 integer)) foo LEFT JOIN (SELECT users_table.value_2 FROM public.users_table, public.events_table WHERE ((users_table.user_id = events_table.user_id) AND (events_table.event_type = ANY (ARRAY[5, 6, 7, 8])))) bar ON ((foo.value_2 = bar.value_2)))
 ERROR:  cannot pushdown the subquery
 DETAIL:  Complex subqueries and CTEs cannot be in the outer part of the outer join
+-- Aggregates in subquery without partition column can be planned recursively
+-- unless there is a reference to an outer query
+SELECT
+    * 
+FROM
+    users_table 
+WHERE
+    user_id IN 
+    (
+        SELECT
+            SUM(events_table.user_id) 
+        FROM
+            events_table 
+        WHERE
+            users_table.user_id = events_table.user_id 
+    )
+;
+ERROR:  cannot push down this subquery
+DETAIL:  Aggregates without group by are currently unsupported when a subquery references a column from another query
+-- Having qual without group by on partition column can be planned recursively
+-- unless there is a reference to an outer query
+SELECT
+    * 
+FROM
+    users_table 
+WHERE
+    user_id IN 
+    (
+        SELECT
+            SUM(events_table.user_id) 
+        FROM
+            events_table 
+        WHERE
+            events_table.user_id = users_table.user_id 
+        HAVING
+            MIN(value_2) > 2 
+    )
+;
+ERROR:  cannot push down this subquery
+DETAIL:  Having qual without group by on partition column is currently unsupported when a subquery references a column from another query
 SET client_min_messages TO DEFAULT;
 DROP SCHEMA not_supported CASCADE;
 NOTICE:  drop cascades to table users_table_local

src/test/regress/sql/subqueries_not_supported.sql

@@ -131,7 +131,47 @@ FROM
     	(SELECT users_table.value_2 FROM users_table, events_table WHERE users_table.user_id = events_table.user_id AND event_type IN (5,6,7,8)) as bar
 	ON(foo.value_2 = bar.value_2);
 
+
+-- Aggregates in subquery without partition column can be planned recursively
+-- unless there is a reference to an outer query
+SELECT
+    * 
+FROM
+    users_table 
+WHERE
+    user_id IN 
+    (
+        SELECT
+            SUM(events_table.user_id) 
+        FROM
+            events_table 
+        WHERE
+            users_table.user_id = events_table.user_id 
+    )
+;
+
+
+-- Having qual without group by on partition column can be planned recursively
+-- unless there is a reference to an outer query
+SELECT
+    * 
+FROM
+    users_table 
+WHERE
+    user_id IN 
+    (
+        SELECT
+            SUM(events_table.user_id) 
+        FROM
+            events_table 
+        WHERE
+            events_table.user_id = users_table.user_id 
+        HAVING
+            MIN(value_2) > 2 
+    )
+;
+
 SET client_min_messages TO DEFAULT;
 
 DROP SCHEMA not_supported CASCADE;
-SET search_path TO public;
+SET search_path TO public;