SQL:从两个相关表中选择最大值

如果我没有记错的话,你要:为每个咖啡馆找服务员先用(最早) HiredDate CreatedDate . 因此,对于Oracle(可能还有SQL Server),可以这样:

SELECT *
FROM   (
  SELECT w.*,
         d.*,
         ROW_NUMBER() OVER ( PARTITION BY CafeID
                             ORDER BY w.HiredDate ASC,
                                      d.CreatedDate ASC ) AS rn
  FROM   Waiter w
         INNER JOIN WaiterDetail d
         ON ( w.WaiterId = d.WaiterId )
)
WHERE  rn = 1;