Fix some comments and error messages

createas.c

@@ -895,8 +895,9 @@ check_ivm_restriction_walker(Node *node, check_ivm_restriction_context *context)
 				/*
 				 * additional restriction checks for exists subquery
 				 *
-				 * When contain EXISTS clauses, and it has a column refernces
+				 * If the query has any EXISTS clauses and columns in them refer to
-				 * a table outside, its column must be included by target list.
+				 * columns in tables in the output query, those columns must be
+				 * included in the target list.
 				 */
 				if (context->exists_qual_vars != NIL && context->sublevels_up == 0)
 				{
@@ -1019,7 +1020,8 @@ check_ivm_restriction_walker(Node *node, check_ivm_restriction_context *context)
 		case T_Var:
 			{
 				Var	*variable = (Var *) node;
-				/* Currently, only EXISTS clause is allowed here.
+				/*
+				 * Currently, only EXISTS clause is allowed here.
 				 * If EXISTS subquery refers to vars of the upper query, collect these vars.
 				 */
 				if (variable->varlevelsup > 0 && context->in_exists_subquery)
@@ -1028,18 +1030,18 @@ check_ivm_restriction_walker(Node *node, check_ivm_restriction_context *context)
 			}
 		case T_SubLink:
 			{
-				/* Now, EXISTS clause is supported only */
+				/* Currently, EXISTS clause is supported only */
 				Query *subselect;
 				SubLink	*sublink = (SubLink *) node;
 				if (sublink->subLinkType != EXISTS_SUBLINK)
 					ereport(ERROR,
 							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 							 errmsg("this query is not allowed on incrementally maintainable materialized view"),
-							 errhint("subquery in WHERE clause only supports subquery with EXISTS clause")));
+							 errhint("sublink only supports subquery with EXISTS clause in WHERE clause")));
 				if (context->sublevels_up > 0)
 					ereport(ERROR,
 							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-							 errmsg("nested subquery is not supported on incrementally maintainable materialized view")));
+							 errmsg("nested sublink is not supported on incrementally maintainable materialized view")));
 
 				subselect = (Query *)sublink->subselect;
 				/* raise ERROR if the sublink has CTE */

expected/pg_ivm.out

@@ -827,22 +827,24 @@ SELECT create_immv('mv_ivm_subquery', 'SELECT a.i,a.j FROM mv_base_a a, (SELECT
 ERROR:  DISTINCT clause in nested query are not supported on incrementally maintainable materialized view
 SELECT create_immv('mv_ivm_subquery', 'SELECT i,j FROM mv_base_a WHERE i IN (SELECT i FROM mv_base_b WHERE k < 103 )');
 ERROR:  this query is not allowed on incrementally maintainable materialized view
-HINT:  subquery in WHERE clause only supports subquery with EXISTS clause
+HINT:  sublink only supports subquery with EXISTS clause in WHERE clause
 SELECT create_immv('mv_ivm_subquery', 'SELECT i,j, (SELECT k FROM mv_base_b LIMIT 1) FROM mv_base_a a');
 ERROR:  this query is not allowed on incrementally maintainable materialized view
-HINT:  subquery in WHERE clause only supports subquery with EXISTS clause
+HINT:  sublink only supports subquery with EXISTS clause in WHERE clause
 SELECT create_immv('mv_ivm_subquery', 'SELECT i,j, (SELECT k FROM mv_base_b LIMIT 1) + 1 FROM mv_base_a a');
 ERROR:  this query is not allowed on incrementally maintainable materialized view
-HINT:  subquery in WHERE clause only supports subquery with EXISTS clause
+HINT:  sublink only supports subquery with EXISTS clause in WHERE clause
 SELECT create_immv('mv_ivm_subquery', 'SELECT * FROM generate_series(1, (SELECT k FROM mv_base_b LIMIT 1)) AS v');
 ERROR:  this query is not allowed on incrementally maintainable materialized view
-HINT:  subquery in WHERE clause only supports subquery with EXISTS clause
+HINT:  sublink only supports subquery with EXISTS clause in WHERE clause
 SELECT create_immv('mv_ivm_subquery', 'SELECT a.j FROM mv_base_a a WHERE EXISTS(SELECT 1 FROM mv_base_b b WHERE a.i = b.i)');
 ERROR:  this query is not allowed on incrementally maintainable materialized view
 HINT:  targetlist must contain vars that are referred to in EXISTS subquery
 SELECT create_immv('mv_ivm_subquery', 'SELECT a.i,a.j FROM mv_base_a a WHERE EXISTS(SELECT 1 FROM mv_base_b b WHERE a.i = b.i) OR a.i > 2');
 ERROR:  this query is not allowed on incrementally maintainable materialized view
 HINT:  OR or NOT conditions and EXISTS condition are not used together
+SELECT create_immv('mv_ivm_subquery', 'SELECT a.j FROM mv_base_a a WHERE EXISTS(SELECT 1 FROM mv_base_a a2 WHERE EXISTS(SELECT 1 FROM mv_base_b b WHERE a2.i = b.i))');
+ERROR:  nested sublink is not supported on incrementally maintainable materialized view
 -- support join subquery in FROM clause
 BEGIN;
 SELECT create_immv('mv_ivm_join_subquery', 'SELECT i, j, k FROM ( SELECT i, a.j, b.k FROM mv_base_b b INNER JOIN mv_base_a a USING(i)) tmp');

matview.c

@@ -1587,11 +1587,6 @@ rewrite_query_for_distinct_and_aggregates(Query *query, ParseState *pstate)
 	return query;
 }
 
-/*
- * rewrite_query_for_exists_subquery
- *
- * Rewrite EXISTS sublink in WHERE to LATERAL subquery
- */
 static Query *
 rewrite_exists_subquery_walker(Query *query, Node *node, int *count)
 {
@@ -1725,6 +1720,21 @@ rewrite_exists_subquery_walker(Query *query, Node *node, int *count)
 	return query;
 }
 
+/*
+ * rewrite_query_for_exists_subquery
+ *
+ * Rewrite EXISTS sublink in WHERE to LATERAL subquery
+ * For example, rewrite
+ *   SELECT t1.* FROM t1
+ *   WHERE EXISTS(SELECT 1 FROM t2 WHERE t1.key = t2.key)
+ * to
+ *   SELECT t1.*, ex.__ivm_exists_count_0__
+ *   FROM t1, LATERAL(
+ *     SELECT 1, COUNT(*) AS __ivm_exists_count_0__
+ *     FROM t2
+ *     WHERE t1.key = t2.key
+ *     HAVING __ivm_exists_count_0__ > 0) AS ex
+ */
 Query *
 rewrite_query_for_exists_subquery(Query *query)
 {

sql/pg_ivm.sql

@@ -270,6 +270,7 @@ SELECT create_immv('mv_ivm_subquery', 'SELECT i,j, (SELECT k FROM mv_base_b LIMI
 SELECT create_immv('mv_ivm_subquery', 'SELECT * FROM generate_series(1, (SELECT k FROM mv_base_b LIMIT 1)) AS v');
 SELECT create_immv('mv_ivm_subquery', 'SELECT a.j FROM mv_base_a a WHERE EXISTS(SELECT 1 FROM mv_base_b b WHERE a.i = b.i)');
 SELECT create_immv('mv_ivm_subquery', 'SELECT a.i,a.j FROM mv_base_a a WHERE EXISTS(SELECT 1 FROM mv_base_b b WHERE a.i = b.i) OR a.i > 2');
+SELECT create_immv('mv_ivm_subquery', 'SELECT a.j FROM mv_base_a a WHERE EXISTS(SELECT 1 FROM mv_base_a a2 WHERE EXISTS(SELECT 1 FROM mv_base_b b WHERE a2.i = b.i))');
 
 -- support join subquery in FROM clause
 BEGIN;
@@ -379,6 +380,7 @@ ROLLBACK;
 --- disallow not-simple CTE
 SELECT create_immv('mv_cte_fail', 'WITH b AS (SELECT i, COUNT(*) FROM mv_base_b GROUP BY i) SELECT a.i,a.j FROM mv_base_a a, b WHERE a.i = b.i');
 SELECT create_immv('mv_cte_fail', 'WITH b AS (SELECT DISTINCT i FROM mv_base_b) SELECT a.i,a.j FROM mv_base_a a, b WHERE a.i = b.i');
+SELECT create_immv('mv_cte_fail', 'WITH a AS (SELECT i, j FROM mv_base_a) SELECT a.i,a.j FROM a WHERE EXISTS(WITH b AS (SELECT i FROM mv_base_b) SELECT 1 FROM b WHERE a.i = b.i)');
 
 -- unreferenced CTE
 SELECT create_immv('mv_cte_fail', 'WITH b AS (SELECT * FROM mv_base_b) SELECT * FROM mv_base_a a');