SQL：如果满足条件，则选择满足条件的所有行，如果不满足，则仅选择特定的nuber行

Question

我对我需要编写的SQL Server 2005查询有要求，这使我难以完成它。 我会简化很多，但本质是，如果客户没有比某个特定日期更新的账单，我需要从该客户的最新账单中选择最多3个。 但是，如果他们在该截止日期之后有帐单，则只需显示其中任何帐单即可。

因此，如果我的截止日期是2010年1月1日，而我的数据如下：

ClaimID ClientID    BillingDate
1           1          March 12, 2010
2           1          June 3, 2010
3           1          January 5, 2008
4           1          February 9, 2011
5           1          May 19, 2005
6           2          November 20, 2005
7           2          October 5, 2009
8           3          January 4, 1999
9           3          July 8, 1997
10         3          May 7, 2010
11         3          August 6, 1999
12         4          May 25, 2000
13         4          April 1, 2005
14         4          March 9, 2009
15         4          December 5, 2007
16         4          December 19, 1998
17         4          June 3, 2006

然后我要选择：

ClaimID ClientID    BillingDate
1           1          March 12, 2010
2           1          June 3, 2010
4           1          February 9, 2011
6           2          November 20, 2005
7           2          October 5, 2009
10         3          May 7, 2010
14         4          March 9, 2009
15         4          December 5, 2007
17         4          June 3, 2006

有人有想法么？ 谢谢

Answer 1

1. 按BillingDate降序排列每个客户的行。

2. 对于每个客户，输出以下日期之一：

   • 比截止日期更新，或者

   • 属于排名最高的3个。

查询：

;WITH ranked AS (
  SELECT
    *,
    rownum = ROW_NUMBER() OVER (PARTITION BY ClientID ORDER BY BillingDate DESC)
  FROM Billings
)
SELECT ClaimID, ClientID, BillingDate
FROM ranked
WHERE BillingDate > @CutOffDate OR rownum BETWEEN 1 AND 3

Answer 2

您可以使用UNION ALL合并两个查询的结果：

SELECT *
FROM MyTable
WHERE BillingDate > '1-Jan-2010'

UNION ALL

SELECT *
FROM MyTable T1
WHERE NOT EXISTS (SELECT *
                  FROM MyTable T2
                  WHERE T1.ClientID = T2.ClientID AND T2.BillingDate > '1-Jan-2010')
AND ClaimID IN (SELECT TOP 3 T3.ClaimID
                FROM MyTable T3
                WHERE T1.ClientID = T3.ClientID
                ORDER BY T3.BillingDate DESC)

Answer 3

这样的事情应该可以解决您的问题？ 您甚至可以将其作为子选择

select ClaimID, ClientID, BillingDate
from bills
where BillingDate > @cutoffDate
UNION ALL
select ClaimID, ClientID, BillingDate
from bills a
where not exists (select 1 from bills b
         where b.ClientId = a.ClientId
           and b.BillingDate > @cutoffDate)
  and 3 >       (select count(1) from bills b
                 where b.ClientId = a.ClientId
                   and b.BillingDate>a.BillingDate)