[#MDEV-19956] Queries with subqueries containing UNION are not parsed

The following query

SELECT ((SELECT a FROM t1 LIMIT 2) UNION (SELECT a FROM t2 LIMIT 2) LIMIT 1) AS r FROM t1 AS t;

returns syntax error message in 10.4:

ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'UNION (SELECT a FROM t2 LIMIT 2) LIMIT 1) AS r FROM t1 AS t' at line 1

Reprodicible in with the following test case

CREATE TABLE t1 (a int);

INSERT INTO t1 VALUES(1),(2),(3),(4);

CREATE TABLE t2 (a int);

INSERT INTO t2 VALUES (4),(5),(6),(7);

SELECT ((SELECT a FROM t1 LIMIT 2) UNION (SELECT a FROM t2 LIMIT 2) LIMIT 1) AS r FROM t1 AS t;

10.3 and probably all prior versions return the same error message.
MySQL-8.0 returns a proper result:

mysql> SELECT ((SELECT a FROM t1 LIMIT 2) UNION (SELECT a FROM t2 LIMIT 2) LIMIT 1) AS r FROM t1 AS t;

+------+

| r    |

+------+

|    1 |

|    1 |

|    1 |

|    1 |

+------+

This query with a subquery in the WHERE clause also failed to be parsed:

MariaDB [test]> SELECT * FROM t1 WHERE t1.a IN ((SELECT a FROM t1) UNION (SELECT a FROM t2));

ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'UNION (SELECT a FROM t2))' at line 1

10.3 returns the same error message.

MySQL-8.0 is ok with the above query:

mysql> SELECT * FROM t1 WHERE t1.a IN ((SELECT a FROM t1) UNION (SELECT a FROM t2));

+------+

| a    |

+------+

|    1 |

|    2 |

|    3 |

|    4 |

+------+

[MDEV-19956] Queries with subqueries containing UNION are not parsed Created: 2019-07-05 Updated: 2019-10-04 Resolved: 2019-10-04
Status:	Closed
Project:	MariaDB Server
Component/s:	Parser
Affects Version/s:	10.4
Fix Version/s:	10.4.9, 10.5.0

[MDEV-19956] Queries with subqueries containing UNION are not parsed Created: 2019-07-05 Updated: 2019-10-04 Resolved: 2019-10-04