一个简单的SQL语句

select
sum(case a when 0 then b else 0 end) as qty1,
sum(case a when 1 then b else 0 end) as qty2,
sum(b) - qty1 - qty2 as qty3  //qty3我是想实现这样的功能，但我知道这样写肯定不对，不知道怎么能实现？
from table1
group by...

---

SQL code:
select
sum(case a when 0 then b else 0 end) as qty1,
sum(case a when 1 then b else 0 end) as qty2,
sum(b) - sum(case a when 0 then b else 0 end)-sum(case a when 1 then b else 0 end) as qty3
from table1
group by...

---

sum(b) - qty1 - qty2 as qty3
等同于
sum(case a when 0 then 0 when 1 then 0 else b end) as qty3

---

sum(b) - qty1 - qty2 as qty3 替换成sum(b)-sum(case when a=0 or a=1 then b else 0)

---

或者：

select qty1,qty2,b-qty1-qty2
from(
select
sum(case a when 0 then b else 0 end) as qty1,
sum(case a when 1 then b else 0 end) as qty2,
sum(b) as b
from table1
group by..) b

---

就这个就可以了，看起来清爽，呵呵，谢谢各位

引用

sum(b) - qty1 - qty2 as qty3
等同于
sum(case a when 0 then 0 when 1 then 0 else b end) as qty3

---

select
sum(case a when 0 then b else 0 end) as qty1,
sum(case a when 1 then b else 0 end) as qty2,
sum(b) - qty1 - qty2 as qty3  //qty3我是想实现这样的功能，但我知道这样写肯定