SQL 查询横表变竖表

首先是三张表， CNo对应的是课程，在这里我就粘贴了。            

                              主表

                 人名表

按照常规查询

SELECT s.SName, c.CName,s2.SCgrade

  FROM S s INNER JOIN SC s2 ON s2.SNo = s.SNo INNER JOIN C c ON c.CNo = s2.CNo

那么结果是这样的

但是这是横表 不是我想看到的结果。

我们要看到这样的结果：

那么怎么办呢？

   第一种写法：SELECT w.SName,

   sum(case when  w.CNo= 1 then w.SCgrade   ELSE 0 END) AS '语文',

    sum(case  WHEN w.CNo =2 THEN  w.SCgrade  ELSE   0 END) AS '数学',

  sum(case when  w.CNo= 3 then w.SCgrade  ELSE  0 END) AS '英语'

FROM

(SELECT s.SNo,s.SName, s2.CNo, s2.SCgrade  FROM s s INNER JOIN SC s2 ON s2.SNo = s.SNo WHERE s.SNo IN (SELECT c.SNo  FROM sc c GROUP BY c.SNo ))

AS w GROUP BY w.SName

  

   第二种写法： SELECT s.SName,

   sum(case when  s2.CNo= 1 then s2.SCgrade   ELSE 0 END) AS '语文',

    sum(case  WHEN s2.CNo =2 THEN  s2.SCgrade  ELSE   0 END) AS '数学',

  sum(case when  s2.CNo= 3 then s2.SCgrade  ELSE  0 END) AS '英语'

FROM

 S s INNER JOIN SC s2 ON s2.SNo = s.SNo

INNER JOIN C c ON c.CNo = s2.CNo

 GROUP BY s.SNo,

 s.SName