MySQL更新运行缓慢

Question

以下查询：

 UPDATE `zydushr`.`performance`  AS a1 , `zydusquiz`.`performance` AS a2 
 SET a1.`Sales` = a2.`AchievementHQ` WHERE a1.`EmpNo` = a2.`EmpNo` 
 AND a1.`Month` = a2.`Month` AND a1.`Year` = a2.`Year` ; 

运行得很慢。我怎样才能加快速度？

注意：我已经创建了索引。

Answer 1

UPDATE 
`zydushr`.`performance`  AS a1 
JOIN `zydusquiz`.`performance` AS a2 
ON a1.`EmpNo` = a2.`EmpNo` 
 AND a1.`Month` = a2.`Month` 
 AND a1.`Year` = a2.`Year` 
SET a1.`Sales` = a2.`AchievementHQ` 

Answer 2

对于速度，您需要复合索引：

INDEX(emp_no, year, month)

与INDEX(emp_no), INDEX(year), INDEX(month)相同。

为日期和时间组件设置单独的列通常是不好的做法。