mysql的in會讓索引失效嗎？不會！ 看結(jié)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: 0

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 | range | g | g | 34 | NULL | 3 | 100.00 | Using index condition |

+----+-------------+-------------+------------+-------+---------------+------+---------+------+------+----------+-----------------------+

1 row in set, 1 warning (0.00 sec)

mysql>

順便說下，in查出的結(jié)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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