50个查询系列-第13个查询：把“SC”表中“叶平”老师教的课的成绩都更改为此课程的平均成绩；

时间：2021-08-12 21:36:15
UPDATE tblscore SET tblscore.Score=

(

-- 这里开始算叶平的平均值

SELECT AVG(tt.aa) FROM

(

SELECT  tblscore.Score aa FROM tblscore WHERE

tblscore.CourseId=

( 

SELECT tblcourse.CourseId FROM tblcourse WHERE tblcourse.CourseId=(

SELECT tblteacher.TeaId FROM tblteacher WHERE tblteacher.TeaName='叶平' )

))tt -- 算出叶平教得课程的平均值

 )

 WHERE tblscore.CourseId=

 (SELECT tblcourse.CourseId FROM tblcourse WHERE tblcourse.CourseId=(

SELECT tblteacher.TeaId FROM tblteacher WHERE tblteacher.TeaName='叶平' ))-- 叶平上课的id

答案的写法：

Select * Into Sc From tblScore

 go

 Update Sc Set Score=(Select Avg(Score) From tblScore s1 Where s1.CourseId=sc.CourseId)

  Where CourseId IN

   (Select CourseId From tblCourse cs INNER JOIN tblTeacher tc ON cs.TeaID=tc.TeaID WHERE TeaName ='叶平')

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