Bug involving subqueries and the OR optimization
|User & Date:||dan 2010-12-06 16:01:30|
- Change comment to:
SELECT statements can return incorrect results in certain cases where the following are true:
- The query is a join,
- The query takes advantage of the OR optimization,
- At least one branch of the optimized OR expression in the WHERE clause involves a subquery.
- At least one branch of the optimized OR expression in the WHERE clause refers to a column of a table other than the table to which the OR optimization applies.
CREATE TABLE t1(a); INSERT INTO t1 VALUES('A'); CREATE INDEX i1 ON t1(a); CREATE TABLE t2(b); INSERT INTO t2 VALUES('B'); CREATE TABLE t3(c); INSERT INTO t3 VALUES('C'); SELECT * FROM t1, t2 WHERE (a='A' AND b='X') OR (a='A' AND EXISTS (SELECT * FROM t3 WHERE c='C'))
The bug causes the query above returns zero rows instead of the expected result - one row.
This bug was discovered in a real application and reported on the mailing list. Bisection reveals that it was introduced on 2009-08-13 by commit [86a06dd049]. It first appeared in release 3.6.18.
- Change detected to "Application_Fault"
- Change foundin to "3.7.3"
- Change severity to "Important"
- Change status to "Open"
- Change subsystem to "Code_Generator"
- Change title to "Bug involving subqueries and the OR optimization"
- Change type to "Code_Defect"