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mysql的in會讓索引失效嗎？不會！看結果：

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>

總結

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