Firebird摘要字段计算

Question

我想这样做：

select 
  id, 
  sum(field1) as a,
  sum(field2) as b,
  a - b as result group by id;

但火鸟显示“列未知。”。第“a - b行”中的错误。怎么做到这一点。感谢..

Answer 1

在减法中也写出sum()，即

select 
  id, 
  sum(field1) as a,
  sum(field2) as b,
  sum(field1) - sum(field2) as result 
group by id;