索引优化实战三

一索引列上不能有范围查询

存储引擎不能使用索引中范围条件右边的列。

二实战

# 全值匹配我最爱
mysql> explain select * from staffs where name = 'July' and age=15 and pos='dev';
+----+-------------+--------+------------+------+-------------------------+-------------------------+---------+-------------------+------+----------+-------+
| id | select_type | table  | partitions | type | possible_keys           | key                     | key_len | ref               | rows | filtered | Extra |
+----+-------------+--------+------------+------+-------------------------+-------------------------+---------+-------------------+------+----------+-------+
|  1 | SIMPLE      | staffs | NULL       | ref  | index_staffs_nameAgePos | index_staffs_nameAgePos | 140     | const,const,const |    1 |   100.00 | NULL  |
+----+-------------+--------+------------+------+-------------------------+-------------------------+---------+-------------------+------+----------+-------+
1 row in set, 1 warning (0.00 sec)
# 存储引擎不能使用索引中范围条件右边的列：name用于索引，age用于排序，post不能用于索引。
mysql> explain select * from staffs where name = 'July' and age>15 and pos='dev';
+----+-------------+--------+------------+-------+-------------------------+-------------------------+---------+------+------+----------+-----------------------+
| id | select_type | table  | partitions | type  | possible_keys           | key                     | key_len | ref  | rows | filtered | Extra                 |
+----+-------------+--------+------------+-------+-------------------------+-------------------------+---------+------+------+----------+-----------------------+
|  1 | SIMPLE      | staffs | NULL       | range | index_staffs_nameAgePos | index_staffs_nameAgePos | 78      | NULL |    1 |    33.33 | Using index condition |
+----+-------------+--------+------------+-------+-------------------------+-------------------------+---------+------+------+----------+-----------------------+
1 row in set, 1 warning (0.00 sec)