SQL查询横表变竖表简析
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SQL查询横表变竖表简析
首先是三张表, CNo对应的是课程,在这里我就粘贴了。
www.2cto.com
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 ))
s.SNo WHERE s.SNo IN (SELECT c.SNo FROM sc c GROUP BY c.SNo ))
AS w GROUP BY w.SName www.2cto.com
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
这是我工作遇到过得情况,总结下来。如果有遇到这种情况的话可以参考下。
作者 小马的酒吧
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