SQL中关于条件Count的查询语句问题

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

如何合并这三个查询？
得到一个查询结果：
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