select * from
(
select isnull(a, 0) as exp1, (isnull(b, 0) + isnull(c, 0)) as exp2 from table1
) awhere a.exp1 <> a.exp2
(
select isnull(a, 0) as exp1, (isnull(b, 0) + isnull(c, 0)) as exp2 from table1
) awhere a.exp1 <> a.exp2
where (isnull(a, 0) <> isnull(b, 0) + isnull(c, 0))第一步:在table1中找出符合where条件的纪录
第二步:将字段、表达式赋予别名
所以在第一步时还没有Expr1、Expr2