MySQL查询速度慢…有时候

+----+-------------+---------+------+---------------------------+---------------------+---------+------------------+------+--------------------------------------+
| id | select_type | table   | type | possible_keys             | key                 | key_len | ref              | rows | Extra                                |
+----+-------------+---------+------+---------------------------+---------------------+---------+------------------+------+--------------------------------------+
|  1 | SIMPLE      | v       | ref  | PRIMARY,cand_visitor_omit | cand_visitor_omit   | 4       | const            |    1 | Using where                          |
|  1 | SIMPLE      | current | ref  | visitorid_visittime       | visitorid_visittime | 8       | test.v.visitorid |    2 | Using where; Using index             |
|  1 | SIMPLE      | earlier | ref  | visitorid_visittime       | visitorid_visittime | 8       | test.v.visitorid |    2 | Using where; Using index; Not exists |
+----+-------------+---------+------+---------------------------+---------------------+---------+------------------+------+--------------------------------------+

以这种方式更改索引也会使访问者(visitorid)上的其他单列索引变得多余,因此您可以删除该索引.

（编辑：ASP站长）

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