Wrong result (NULL instead of a value) with no matching rows, subquery in FROM and HAVING
Affects | Status | Importance | Assigned to | Milestone | |
---|---|---|---|---|---|
MariaDB |
Fix Released
|
Medium
|
Timour Katchaounov |
Bug Description
The following query
SELECT MAX(a), ( SELECT 1 FROM t2 ) AS bb FROM t1
with 0 rows in t1 and 1 row in t2 produces NULL, NULL on maria/5.3 and maria/5.5. Same happens if t1 is not empty, but the outer SELECT has an impossible WHERE condition. t2 can have more rows too, in which case a subquery should use an aggregate function, e.g. SUM.
The same query without t2 produces NULL, 1;
SELECT MAX(a), ( SELECT 1 ) AS bb FROM t1
maria-5.1, maria-5.2, mysql-5.1, mysql-5.5, mysql-trunk, postgres-8.4.7 return NULL, 1 for both queries.
Reproducible with MyISAM and Aria, but not InnoDB.
Reproducible with the default optimizer_switch as well as with all OFF values (except for in_to_exists required to execute the query).
EXPLAIN (with in_to_exists=on, everything else OFF):
id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY t1 system NULL NULL NULL NULL 0 0.00 const row not found
2 SUBQUERY t2 system NULL NULL NULL NULL 1 100.00
Warnings:
Note 1003 select max(NULL) AS `MAX(a)`,(select 1 from dual) AS `bb` from `test`.`t1`
# Test case:
SET optimizer_
CREATE TABLE t1 (a INT) ENGINE=MyISAM;
CREATE TABLE t2 (b INT) ENGINE=MyISAM;
INSERT INTO t2 VALUES (1);
# Either t1 is empty, or SELECT has an impossible condition.
# Either t2 has 1 row, or an aggregate function, e.g. SUM, is used in the subquery.
SELECT MAX(a), ( SELECT 1 FROM t2 ) AS bb FROM t1;
# End of test case
# Expected result:
#
# MAX(a) bb
# NULL 1
# Actual result:
#
# MAX(a) bb
# NULL NULL
Related branches
summary: |
Wrong result (NULL instead of a value) with no matching rows, subquery - in FROM and HAVING; crash on 5.2 + in FROM and HAVING |
description: | updated |
Changed in maria: | |
status: | New → In Progress |
Changed in maria: | |
status: | In Progress → Fix Committed |
Changed in maria: | |
status: | Fix Committed → Fix Released |
Reviewing...