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:

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