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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