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MDEV-19134: EXISTS() slower if ORDER BY is defined

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Step #2: "[ORDER BY ...] LIMIT n" should not prevent EXISTS-to-IN
conversion, as long as
- the LIMIT clause doesn't have OFFSET
- the LIMIT is not "LIMIT 0".
This commit is contained in:
Sergei Petrunia
2019-05-10 12:47:44 +03:00
parent b1f828a82a
commit d448cfc92a
4 changed files with 82 additions and 20 deletions
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2
mysql-test/main/subselect_innodb.result
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@ -311,7 +311,7 @@ EXPLAIN SELECT 1 FROM t1 WHERE NOT EXISTS
(SELECT 1 FROM t2 WHERE d = (SELECT d FROM t2 WHERE a >= 1) ORDER BY d);
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 ALL NULL NULL NULL NULL 1 Using where
2 DEPENDENT SUBQUERY t2 eq_ref PRIMARY,d PRIMARY 1 func 1 Using where
2 DEPENDENT SUBQUERY t2 unique_subquery PRIMARY,d PRIMARY 1 func 1 Using where
3 DEPENDENT SUBQUERY t2 index NULL d 2 NULL 1 Using index
DROP TABLE t2;
CREATE TABLE t2 (b INT, c INT, UNIQUE KEY (b), UNIQUE KEY (b, c )) ENGINE=INNODB;