如何在SQL语句的Select子句中引用子查询

我有一个SQL查询，如下所示：

DECLARE @I int

SET @I = (SELECT W.PMon FROM WHouse.dbo.Rundate AS W)

SELECT L.ACCOUNT, 
L.ID,
L.OPENDATE, 
L.ORIGINALBALANCE, 
L.BALANCE, 
L.DUEDATE,
(SELECT N.BIRTHDATE FROM Sym.dbo.NAME AS N WHERE N.Account = L.Account and  N.ORDINAL = 0) AS 'PBD',
(SELECT N.BIRTHDATE FROM Sym.dbo.LOANNAME AS N WHERE L.Account = N.Account and L.ID = N.PARENTID and N.TYPE IN (01, 16, 20, 21)) AS 'JBD',
L.CREDITSCORE

FROM Sym.dbo.Loan AS L
JOIN Sym.dbo.Account AS A
ON L.Account = A.Account
WHERE L.TYPE IN (0, 1, 2, 3, 14, 15, 23) and L.BALANCE > 0 and L.CHARGEOFFDATE IS NULL and L.CLOSEDATE IS NULL and A.TYPE <> 5

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在WHERE子句中，如何引用SELECT子句中的子查询进行比较？

如果子查询返回单个值，则只能将其直接放入SELECT子句中。如果要在select子句和where子句的表达式中引用子查询中的列，则需要将子查询放入From子句中，并使用别名。。。或作为联接表，条件在On子句中：

只需将子查询放在From子句中的联接中即可

SELECT L.ACCOUNT, L.ID,L.OPENDATE, 
    L.ORIGINALBALANCE, L.BALANCE, 
    L.DUEDATE, L.CREDITSCORE,
    pbd.Birthdate PBDBirthdate,
    jbd.Birthdate JBDBirthdate
FROM Sym.dbo.Loan AS L
   JOIN Sym.dbo.Account AS A
      ON A.Account = L.Account
   Join Sym.dbo.NAME pbd
      On pbd.Account = L.Account 
         and pbd.ORDINAL = 0
    Join Sym.dbo.LOANNAME jbd
      On jbd.Account = L.Account 
         and jbd.PARENTID = L.ID
         and jbd.TYPE IN (01, 16, 20, 21)       
WHERE L.TYPE IN (0, 1, 2, 3, 14, 15, 23) 
    and L.BALANCE > 0
    and L.CHARGEOFFDATE IS NULL  

现在，您可以在Select子句表达式中使用别名pbf和/或jbd引用这两个表中的任何列