mysql的in会不会让索引失效?
编程学习 2021-07-05 14:37www.dzhlxh.cn编程入门
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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: 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>
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>
总结
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