使用max函数实现唯一性

原始数据
type  line   amount 
1       a       11
1       b       22
2       a       111
2       b       222
1.列转行
select
   type,
   max(case when line='a' then amount else 0 end ) a,
   max(case when line='b' then amount else 0 end ) b
from test
group by type
结果:
1       11      22
2       111     222

2.不同维度聚合
select
   type,
   case when type=1 then line else '-' end line,
   sum(case when type=1 then 0 else amount end),
   max(case when type=1 then amount else 0 end)
from  test
group by 
   type,
   case when type=1 then line else '-' end
  结果：
1       a       0       11
1       b       0       22
2       -       333     0