Question

我想检索最新版本的最新合约。内部查询有效，但不幸的是，我需要找到一种方法使其在另一个查询中运行时...

这有效：

SELECT * FROM contract t1
WHERE revisionnum = (select max(revisionnum) 
                     from contract t2 
                     where t1.contractnum = t2.contractnum)`

问题是它在select * from contract where语句中，所以它看起来像这样：

SELECT * 
FROM contract 
WHERE -- this line cannot be changed!
exists -- not sure about this
(   SELECT * FROM contract t1
    WHERE revisionnum = (select max(revisionnum) 
                         from contract t2 
                         where t1.contractnum = t2.contractnum) 
)

我该怎么做？

Answer 1

我之前看到有人使用过这样的东西..

SELECT * 
FROM contract 
WHERE 1 = (Select Count(*) 
           From contract c1 
           Where c1.contractnum = contract.contractnum And c1.revisionnum >= contract.revisionnum)

EXISTS 选项

SELECT  *
FROM    [contract]
WHERE   EXISTS ( SELECT c1.contractnum,
                        MAX(c1.revisionnum)
                 FROM   [contract] c1
                 WHERE  c1.contractnum = [contract].contractnum
                 GROUP BY c1.contractnum
                 HAVING MAX(c1.revisionnum) = [contract].revisionnum )

您的原始查询也非常接近..您只是错过了一个小过滤器并使用字段名称别名来指定您指向的表。

SELECT  *
FROM    contract
WHERE   EXISTS -- not sure about this
            ( SELECT    *
                FROM    contract t1
                WHERE   contract.contractnum = t1.contractnum -- filter missing
                        AND contract.revisionnum = (SELECT  MAX  (t2.revisionnum) -- missing table specifier
                                                    FROM    contract t2 
                                                    WHERE t1.contractnum = t2.contractnum) 
            )

Answer 2

SELECT IDENT_CURRENT（[TABLE_NAME]）AS returnID

SQL从结果集T-SQL中获取最新记录

2 个答案: