SQL：如果滿足條件，則選擇滿足條件的所有行，如果不滿足，則僅選擇特定的nuber行

Question

我對我需要編寫的SQL Server 2005查詢有要求，這使我難以完成它。 我會簡化很多，但本質是，如果客戶沒有比某個特定日期更新的賬單，我需要從該客戶的最新賬單中選擇最多3個。 但是，如果他們在該截止日期之后有帳單，則只需顯示其中任何帳單即可。

因此，如果我的截止日期是2010年1月1日，而我的數據如下：

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

然后我要選擇：

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？ 謝謝

Answer 1

1. 按BillingDate降序排列每個客戶的行。

2. 對於每個客戶，輸出以下日期之一：

   • 比截止日期更新，或者

   • 屬於排名最高的3個。

查詢：

;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合並兩個查詢的結果：

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

這樣的事情應該可以解決您的問題？ 您甚至可以將其作為子選擇

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)