请教一个sql 的case 简单用法

有一个数据库表
acc
je     flag  
10       a
20       a
50       b
10       b


现在想用一个语句   吧   flag   =   a   和   b   的分开合计.达到如下效果

a         b
30       60  

我用了

select   a   =   case   flag   = 'a '   then   sum(je)
else   0,
b   =   case   flag   = 'b '   then   sum(je)
else   0
from   acc

这样语法好像有问题,请教该如何写?


------解决方案--------------------

select a = sum(case flag = 'a ' then je else 0 end),
b = sum(case flag = 'b ' then je else 0 end)
from acc
------解决方案--------------------
select (case flag when 'a ' then je else 0) AS b,(case flag when 'b ' then je else 0) AS b
from acc
------解决方案--------------------
select a = sum(case when flag = 'a ' then je
else 0 end),
b =sum(case when flag = 'b ' then je
else 0 end)
from acc
------解决方案--------------------
--建立测试环境
create table #acc(je int,flag varchar(10))
insert #acc(je,flag)
select '10 ', 'a ' union all
select '20 ', 'a ' union all
select '50 ', 'b ' union all
select '10 ', 'b '
go
--执行测试语句
select a = sum(case when flag = 'a ' then je else 0 end),
b = sum(case when flag = 'b ' then je else 0 end)
from #acc
go
--删除测试环境
drop table #acc
go
/*--测试结果
a b
----------- -----------
30 60

(1 row(s) affected)

*/


------解决方案--------------------
select a = case flag = 'a ' then sum(je)
else 0,
b = case flag = 'b ' then sum(je)
else 0
from acc

这样语法好像有问题,请教该如何写?

------
select a=sum(case when flag= 'a ' then je else 0 end),
b=sum(case when flag= 'b ' then je else 0 end)
from acc
------解决方案--------------------
select a = sum(case when flag = 'a ' then je
else 0 end),
b = sum(case when flag = 'b ' then je
else 0)
from acc
------解决方案--------------------
group by 不就行了.
------解决方案--------------------
select sum(case flag when 'a ' then je else 0 end) AS a,sum(case flag when 'b ' then je else 0 end) AS b
from acc
------解决方案--------------------
select a = case when flag = 'a ' then sum(je)
else 0 end ,
b = case when flag = 'b ' then sum(je)
else 0 end
from acc