case when 的简单用法

java群里一哥们问：
怎么把这样一个表[code]
year month amount
1991 1 1.1
1991 2 1.2
1991 3 1.3
1991 4 1.4
1992 1 2.1
1992 2 2.2
1992 3 2.3
1992 4 2.4
查成这样一个结果
year m1 m2 m3 m4
1991 1.1 1.2 1.3 1.4
1992 2.1 2.2 2.3 2.4[/code]

搞了半天才想到 可以用case when

好了 结果如下:
[code]
select year,
sum(case when month=1 then amount end) as m1 ,
sum(case when month=2 then amount end) as m2 ,
sum(case when month=3 then amount end) as m3 ,
sum(case when month=4 then amount end) as m4
from test
GROUP BY year
[/code]
这里sum(case when month=1 then amount end) as m1
如果闲麻烦，那就在拼sql吧 for (int i = 1;i <13 ;i++)......