MySQL的更新運行緩慢

Question

以下查詢：

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` ; 

的運行速度非常慢。我如何加快速度？

注：我已經創建了索引。

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

對於速度，你需要一個複合指數：

INDEX(emp_no, year, month) 

也就是說不一樣INDEX(emp_no), INDEX(year), INDEX(month)。

對日期和時間組件分別設置列通常是不好的做法。