sql过滤别名列的结果

Question

我们如何过滤别名？例如，在下面的查询中，对于别名OLB，如果我们想说WHERE OLB＆gt; 0

SELECT
loan.lnr
,loan.lamount - SUM (memrepay.mprinc) AS OLB
,lstatus

FROM
 loan
  LEFT OUTER JOIN memrepay
  ON loan.lnr = memrepay.lnr

WHERE
loan.tstart >= N'2013-07-07T14:00:00' 

GROUP BY loan.lnr, lamount, lstatus

Order By lnr

Answer 1

使用派生表

select t.* from
(
SELECT
loan.lnr
,loan.lamount - SUM (memrepay.mprinc) AS OLB
,lstatus

FROM
 loan
  LEFT OUTER JOIN memrepay
  ON loan.lnr = memrepay.lnr

WHERE
loan.tstart >= N'2013-07-07T14:00:00' 

GROUP BY loan.lnr, lamount, lstatus
) as t where OLB>0
Order By lnr

或使用HAVING子句并使用表达式

SELECT
loan.lnr
,loan.lamount - SUM (memrepay.mprinc) AS OLB
,lstatus

FROM
 loan
  LEFT OUTER JOIN memrepay
  ON loan.lnr = memrepay.lnr
WHERE
loan.tstart >= N'2013-07-07T14:00:00' 

GROUP BY loan.lnr, lamount, lstatus
HAVING loan.lamount - SUM (memrepay.mprinc) >0
Order By lnr