Mysql 中 case when then else end 用法

SQL 语法如下:

SELECT *,(SELECT CASE 
WHEN score is null then '无记录' 
WHEN score = 1 THEN '优' 
WHEN score = 2 THEN '良' 
WHEN score = 3 THEN '中'
ELSE '差'

END ) as u_score from `user`

查询结果如下: