mysql的in会不会让索引失效?

2020-01-18 20:52:24

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mysql的in会让索引失效吗？不会！看结果：

mysql> desc select * from tb_province where name in ('lily3', 'lily2', 'lily1');+----+-------------+-------------+------------+------+---------------+------+---------+------+--------+----------+-------------+| id | select_type | table    | partitions | type | possible_keys | key | key_len | ref | rows  | filtered | Extra    |+----+-------------+-------------+------------+------+---------------+------+---------+------+--------+----------+-------------+| 1 | SIMPLE   | tb_province | NULL    | ALL | NULL     | NULL | NULL  | NULL | 108780 |  30.00 | Using where |+----+-------------+-------------+------------+------+---------------+------+---------+------+--------+----------+-------------+1 row in set, 1 warning (0.00 sec)mysql> alter table tb_province add index g(name);Query OK, 0 rows affected (0.29 sec)Records: 0 Duplicates: 0 Warnings: 0mysql> desc select * from tb_province where name in ('lily3', 'lily2', 'lily1');+----+-------------+-------------+------------+-------+---------------+------+---------+------+------+----------+-----------------------+| id | select_type | table    | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra         |+----+-------------+-------------+------------+-------+---------------+------+---------+------+------+----------+-----------------------+| 1 | SIMPLE   | tb_province | NULL    | range | g       | g  | 34   | NULL |  3 |  100.00 | Using index condition |+----+-------------+-------------+------------+-------+---------------+------+---------+------+------+----------+-----------------------+1 row in set, 1 warning (0.00 sec)mysql>

顺便说下，in查出的结果，不一定按in排序，如下：

mysql> select * from tb_province where name in ('lily3', 'lily2', 'lily1');+----+-------+-------+------+------+------+------+------+------+------+------+------+------+------+| id | name | score | x  | x1  | x2  | x3  | x4  | x5  | x6  | x7  | x8  | x9  | x10 |+----+-------+-------+------+------+------+------+------+------+------+------+------+------+------+| 1 | lily1 |   1 |  0 |  0 |  0 |  0 |  0 |  0 |  0 |  0 |  0 |  0 |  0 || 2 | lily2 |   2 |  0 |  0 |  0 |  0 |  0 |  0 |  0 |  0 |  0 |  0 |  0 || 3 | lily3 |   3 |  0 |  0 |  0 |  0 |  0 |  0 |  0 |  0 |  0 |  0 |  0 |+----+-------+-------+------+------+------+------+------+------+------+------+------+------+------+3 rows in set (0.00 sec)mysql>

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