多条件聚合函数

Question

如何在mysqlsth这样实现:

select 
sum(B.someField) where B.someIntFild = 1
sum(B.someField) where B.someintFild = 2
from tableA A
inner join tableB B on A.id = B.id
where A.id = 'someId'

是一组上的两个和，但第一个和是针对具有someIntFild = 1和someIntFild = 2的项?

Answer 1

使用条件聚合，例如

sum(case when B.someIntFild = 1 then B.somefield else 0 end) as Col1,
sum(case when B.someIntFild = 2 then B.somefield else 0 end) as Col2

等