SQL的行列转换

Posted 2020-06-14

【一】行转列

1，查询原始的数据

/***这次练习的主题，行转列，列转行***/
select * from Scores

2，得到姓名，通过group by

select Student as ‘姓名‘
from Scores
group by Student
order by Student

3，再加上max， case……when

select Student as ‘姓名‘,
max(case Subject when ‘语文‘ then Score else 0 end) as ‘语文‘ ,--如果这个行是“语文”，就选此行作为列
max(case Subject when ‘英语‘ then Score else 0 end ) as ‘英语‘
from Scores
group by Student
order by Student

 

查看其它资料时，看到另外一种方法，用pivot

--group by, avg/max, pivot。这里用max和avg，结果都一样，有什么区别吗？有点不明白

--参考网上的资料，用法如下

/*

pivot(

　　聚合函数(要转成列值的列名)

　　for 要转换的列

　　in（目标列名）

　　)

*/

select Student as ‘姓名‘,

avg(语文) as ‘语文‘,
avg(英语) as ‘英语‘
from Scores
pivot(
    avg(Score) for Subject 
    in (语文,英语)
    )as NewScores
group by Student
order by Student asc