sql 一练

                                                  sql 的 简单行列转换

   在sql 的运用中，经常用到简单的行列转换。以下是自己 调试的一个小例子。

 

 

  create table mtest(
  sname nvarchar(50),
  subject nvarchar(50),
  course int
)

insert into mtest(sname,subject,course) values('张三','语文',80)
insert into mtest(sname,subject,course) values('张三','数学',81)
insert into mtest(sname,subject,course) values('张三','英语',82)
insert into mtest(sname,subject,course) values('李四','语文',90)
insert into mtest(sname,subject,course) values('李四','数学',91)
insert into mtest(sname,subject,course) values('李四','英语',92)

--select * from mtest
select sname as 姓名,sum(case subject when '语文' then course else 0 end) as '语文',
             sum(case subject when '数学' then course else 0 end) as '数学',
             sum(case subject when '英语' then course else 0 end) as '英语'
        from mtest
        group by sname