Where 子句中的未知列：Mysql 更新查询

Question

这是我的更新查询：

update grade 
  set grade='A'
where (select assignment*0.3+midExam*0.35+finalExam*0.35 as FINALSCORE 
       from taking) >= 85 
  and taking.student_id = grade.student_id 
  and taking.subject_id = grade.subject-id;

结果如下

'where 子句'中的未知列'taking.student_id'

我究竟做错了什么？

Answer 1

taking表在子查询内，然后在子查询外不可见

根据您的需要，您应该使用带有连接的更新

update grade 
INNER JOIN taking ON taking.student_id=grade.student_id
       and taking.subject_id=grade.subject_id 
         and taking.assignment*0.3+taking.midExam*0.35+taking.finalExam*0.35 >= 85
set grade='A'

通用解决方案

您可以尝试为每个年级添加一个案例

update grade 
INNER JOIN taking ON taking.student_id=grade.student_id
       and taking.subject_id=grade.subject_id          
set grade = (case when taking.assignment*0.3+taking.midExam*0.35+taking.finalExam*0.35 >= 85 THEN  'A'
              when taking.assignment*0.3+taking.midExam*0.35+taking.finalExam*0.35 between 60.0 and 84.9 THEN 'B'
              ELSE 'C' END)