derby sql 两个聚合值之间的差异或如何组合两个 sql 语句

Question

以下两个查询自己工作：

select coalesce(sum(shares*cps),0.0)  from 
transactions
where usr = 1
and (type = 'C'
or type  = 'S')

select coalesce(sum(shares*cps),0.0) from 
transactions
where usr = 1
and (type = 'W'
or type  = 'B')

我如何将它们结合起来以获得它们之间的区别？类似于：

select coalesce(sum(a.shares*a.cps),0.0) - coalesce(sum(b.shares*b.cps),0.0)   from 
      (select * from transactions
                where usr = 1
                  and (type = 'C'
                   or type  = 'S')) as a,
      (select * from transactions
                where usr = 1
                  and (type = 'W'
                   or type  = 'B')) as b;

返回值为0。第一次合并returns 200000.00，第二次合并returns 0.00

Answer 1

您可以使用 SYSDUMMY1，一个带有一条记录的虚拟 table，可用于 select 简单值，在这种情况下，两个总和之间的差值：

select 
( select coalesce(sum(shares*cps),0.0)  from 
  transactions
  where usr = 1
  and (type = 'C'
       or type  = 'S')) -
( select coalesce(sum(shares*cps),0.0) from 
  transactions
  where usr = 1
  and (type = 'W'
       or type  = 'B')) as DIFFERENCE
from SYSIBM.SYSDUMMY1

derby sql 两个聚合值之间的差异或如何组合两个 sql 语句

derby sql difference between two aggregate values or how to combine two sql statements

sql

derby