SQL中關於條件Count的查詢語句問題

create table abc(A int,B int) 

Select A,count(B) as total from ABC group by A
Select A,count(B) as total1 from ABC where B > 30 group by A
Select A,count(B) as totlal2 from ABC where B > 20 group by A

 

如何合並這三個查詢？
得到一個查詢結果：
A,total,total1,total2

 

答：

Select A,
count(B) as total,
sum(case when B > 30 then 1 else 0 end) as total1,
sum(case when B > 20 then 1 else 0 end) as total2 
from ABC group by A