Question

SELECT 
    (UserCourseProgress.TimeEnded - UserCourseProgress.TimeStarted) as SecondsSpent,
    UserCourseProgress.UserId 
FROM 
    UserCourseProgress 
    INNER JOIN UserRoles 
    ON UserCourseProgress.UserId = UserRoles.UserId 
       AND (UserRoles.SuperId = '123' OR UserRoles.UserId = '123')

我正在尝试优化此查询，因为它需要太长时间（主要是将数据复制到Tmp表）。结构很简单，一个名为UserCourseProgress的表和另一个名为UserRoles的表，它们都有UserId列共有，我选择属于超级的所有userRoles用户。有什么想法吗？

Answer 1

使用UNION

SELECT
    (UserCourseProgress.TimeEnded - UserCourseProgress.TimeStarted) as SecondsSpent,
    UserCourseProgress.UserId FROM UserCourseProgress 
INNER JOIN UserRoles ON UserCourseProgress.UserId = UserRoles.UserId
    AND UserRoles.SuperId = '123'

UNION

SELECT
    (UserCourseProgress.TimeEnded - UserCourseProgress.TimeStarted) as SecondsSpent,
    UserCourseProgress.UserId FROM UserCourseProgress 
INNER JOIN UserRoles ON UserCourseProgress.UserId = UserRoles.UserId
    AND UserRoles.UserId = '123';

添加INDEX

ALTER TABLE UserCourseProgress ADD INDEX (UserId);
ALTER TABLE UserRoles ADD INDEX (SuperId, UserId);
ALTER TABLE UserRoles ADD INDEX (UserId);

Answer 2

使用EXPLAIN获取查询执行计划。然后，查看更多消耗步骤并在必要时使用索引。

EXPLAIN

MySQL优化查询

2 个答案: