sql - 减去两列为空

Question

我使用以下内容

 select TotalCredits - TotalDebits as Difference
 from 
 (
 select
 (select sum(TOTALAMOUNT) from journal where memberid=48 and CREDIT =1) as TotalCredits,
 (select SUM(totalamount) from Journal where MEMBERID=48 and DEBIT =1) As TotalDebits
 ) temp

这会返回一个与我不同的字段，我遇到的问题是，如果表没有贷项，但有借项，则临时表的 TotalCredits 字段中包含一个 NULL 值，该值禁止进行数学运算。 (Vica Versa 上有积分，但没有借方)我已经尝试过合并，但似乎无法使其工作。

理性地我需要检查是否:

sum(TOTALAMOUNT) from journal where memberid=48 and CREDIT =1 as TotalCredits is 
null then totalcredits = 0 and visa versa

SQL Server 2008

Answer 1

 select ISNULL(TotalCredits,0) - ISNULL(TotalDebits,0) as Difference
 from 
 (
 select
 (select sum(TOTALAMOUNT) from journal where memberid=48 and CREDIT =1) as TotalCredits,
 (select SUM(totalamount) from Journal where MEMBERID=48 and DEBIT =1) As TotalDebits
 ) temp