mysql 删除数据的时候,会不会走索引?

在 mysql 中，如果涉及到的数据超过 20%，将不会使用索引，反之则会。@zxdposter 你这个应该是翻译错了吧

简单实践

数据总条数是: 1602

符合条件sex,city条数: 女, 广州, 604

mysql> explain delete from  test_del_idx where sex="女" and city = "广州";
+----+-------------+--------------+------------+------+---------------+------+---------+------+------+----------+-------------+
| id | select_type | table        | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra       |
+----+-------------+--------------+------------+------+---------------+------+---------+------+------+----------+-------------+
|  1 | DELETE      | test_del_idx | NULL       | ALL  | idx_sex_city  | NULL | NULL    | NULL | 1602 |   100.00 | Using where |
+----+-------------+--------------+------------+------+---------------+------+---------+------+------+----------+-------------+
1 row in set (0.00 sec)

符合条件sex,city条数: 女, 惠州, 6

mysql> explain delete from  test_del_idx where sex="女" and city = "惠州";
+----+-------------+--------------+------------+-------+---------------+--------------+---------+-------------+------+----------+-------------+
| id | select_type | table        | partitions | type  | possible_keys | key          | key_len | ref         | rows | filtered | Extra       |
+----+-------------+--------------+------------+-------+---------------+--------------+---------+-------------+------+----------+-------------+
|  1 | DELETE      | test_del_idx | NULL       | range | idx_sex_city  | idx_sex_city | 773     | const,const |    6 |   100.00 | Using where |
+----+-------------+--------------+------------+-------+---------------+--------------+---------+-------------+------+----------+-------------+
1 row in set (0.00 sec)

实践环境和数据

环境-docker-mysql5.7

表和数据