威凡网全力打造:网页编程、软件开发编程、平面设计、服务器端开发、操作系统等在线学习平台!学编程,上威凡网!
数据库>> Mysql Sqlserver Oracle SQlite Access Sybase SQL其他
当前位置:首页 > 数据库 > Mysql
上一节 下一节
 一:mysql聚合索引

1:mysql 聚合索引

1:

  primary key (`id`),
  unique key `uid` (`uid`,`task_id`)

?

查询:

? ?

mysql> explain select * from user_task where uid = 232;
+----+-------------+-----------+------+---------------+------+---------+-------+------+-------+
| id | select_type | table     | type | possible_keys | key  | key_len | ref   | rows | extra |
+----+-------------+-----------+------+---------------+------+---------+-------+------+-------+
|  1 | simple      | user_task | ref  | uid           | uid  | 4       | const |  206 |       |
+----+-------------+-----------+------+---------------+------+---------+-------+------+-------+

?

? ?

mysql> explain select * from user_task where task_id = 1454;
+----+-------------+-----------+------+---------------+------+---------+------+-------+-------------+
| id | select_type | table     | type | possible_keys | key  | key_len | ref  | rows  | extra       |
+----+-------------+-----------+------+---------------+------+---------+------+-------+-------------+
|  1 | simple      | user_task | all  | null          | null | null    | null | 55917 | using where |
+----+-------------+-----------+------+---------------+------+---------+------+-------+-------------+
1 row in set (0.00 sec)

?

? ?

mysql> explain select * from user_task where task_id = 1454 and uid = 232;
+----+-------------+-----------+-------+---------------+------+---------+-------------+------+-------+
| id | select_type | table     | type  | possible_keys | key  | key_len | ref         | rows | extra |
+----+-------------+-----------+-------+---------------+------+---------+-------------+------+-------+
|  1 | simple      | user_task | const | uid           | uid  | 8       | const,const |    1 |       |
+----+-------------+-----------+-------+---------------+------+---------+-------------+------+-------+
1 row in set (0.00 sec)

?

如果(a, b, c)

查询a ; a b ; a b c 会用到索引

?

所以建立索引的时候 如果要查询 b c ?那么可以 key(b, c)

?

key 和index 不同的是 key 可以有约束 同时会有索引


申明:本教程内容由威凡网编辑整理并提供IT程序员分享学习,如文中有侵权行为,请与站长联系(QQ:254677821)!
上一节 下一节
相关教程  
其他教程  
Mysql
Sqlserver
Oracle
SQlite
Access
Sybase
SQL其他

违法和不良信息举报中心】邮箱:254677821@qq.com
Copyright©威凡网 版权所有 苏ICP备2023020142号
站长QQ:254677821