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  1. MariaDB Server
  2. MDEV-8599

"WHERE varchar_field LIKE temporal_const" does not use range optimizer

        Details

        • Type: Bug
        • Status: Closed
        • Priority: Major
        • Resolution: Fixed
        • Affects Version/s: 10.1
        • Fix Version/s: 10.1.7
        • Component/s: Optimizer
        • Labels:
          None

          Description

          This script:

          DROP TABLE IF EXISTS t1;
CREATE TABLE t1 (a VARCHAR(10) CHARACTER SET latin1, KEY(a)) ENGINE=MyISAM;
INSERT INTO t1 VALUES ('00:00:00');
INSERT INTO t1 VALUES ('00:00:01');
INSERT INTO t1 VALUES ('00:00:02');
INSERT INTO t1 VALUES ('00:00:03');
INSERT INTO t1 VALUES ('00:00:04');
INSERT INTO t1 VALUES ('00:00:05');
INSERT INTO t1 VALUES ('00:00:06');
INSERT INTO t1 VALUES ('00:00:07');
EXPLAIN SELECT * FROM t1 WHERE a LIKE '00:00:00';

          returns

          +------+-------------+-------+-------+---------------+------+---------+------+------+--------------------------+
| id   | select_type | table | type  | possible_keys | key  | key_len | ref  | rows | Extra                    |
+------+-------------+-------+-------+---------------+------+---------+------+------+--------------------------+
|    1 | SIMPLE      | t1    | range | a             | a    | 13      | NULL |    1 | Using where; Using index |
+------+-------------+-------+-------+---------------+------+---------+------+------+--------------------------+

          The index is used to optimize the query.

          Now if I change the EXPLAIN SELECT query to:

          EXPLAIN SELECT * FROM t1 WHERE a LIKE TIME'00:00:00';

          it does not use the index any longer:

          +------+-------------+-------+-------+---------------+------+---------+------+------+--------------------------+
| id   | select_type | table | type  | possible_keys | key  | key_len | ref  | rows | Extra                    |
+------+-------------+-------+-------+---------------+------+---------+------+------+--------------------------+
|    1 | SIMPLE      | t1    | index | a             | a    | 13      | NULL |    8 | Using where; Using index |
+------+-------------+-------+-------+---------------+------+---------+------+------+--------------------------+

          It happens because of this wrong condition in get_mm_leaf:

            if (value->cmp_type() == TIME_RESULT && field->cmp_type() != TIME_RESULT)
    goto end;

          This condition is valid for the comparison operators (<,>,=, etc), but should not be checked for LIKE.

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                  • Assignee:
                    bar Alexander Barkov
                    Reporter:
                    bar Alexander Barkov
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                    Dates

                    • Created:
                      Updated:
                      Resolved: