帮助进行跨多个列的复杂自引用查询

Question

我在处理复杂的（对我来说无论如何）查询时遇到困难。

我正在查询的表有 3 列，ClientID (int Not Null)、ProductID (int Not Null) 和 ExpiryDate (smalldatetime nullable)

给定两个客户端 ID Master 和 Consolidated，我需要执行以下业务逻辑来返回单个数据集:

选择具有较大值的 ClientID 过期产品的失效日期 两个 clientID 的日期都不为空

选择过期时间为空的 ClientID 一次到期的产品的日期 null 且另一个不为 null

选择产品的 MasterID 其中两个到期日期均为空或 两个到期日期相同。

我已经尝试过以下方法，但陷入困境...

Create Table #ProductSub (ClientID int NOT NULL, 
                          ProductID int NOT NULL, 
                          ExpiryDate smalldatetime)  

/* In real life there is a Clustered Primary Key On ClientID and ProductID
   Load Up Some Test Data */  

  Insert into #ProductSub  Values (1, 100, null)
  Insert into #ProductSub  Values (2, 100, null)
  Insert into #ProductSub  Values (1, 101, null)
  Insert into #ProductSub  Values (2, 102, null)
  Insert into #ProductSub  Values (1, 200, null)
  Insert into #ProductSub  Values (2, 200, '2009-01-01')
  Insert into #ProductSub  Values (1, 300, '2009-01-01')
  Insert into #ProductSub  Values (2, 300, null)
  Insert into #ProductSub  Values (1, 400, '2009-01-01')
  Insert into #ProductSub  Values (2, 400, '2008-01-01')
  Insert into #ProductSub  Values (1, 500, '2008-01-01')
  Insert into #ProductSub  Values (2, 500, '2009-01-01')
  Insert into #ProductSub  Values (1, 600, '2009-01-01')
  Insert into #ProductSub  Values (2, 600, '2009-01-01')  

 --Select * from #ProductSub  

  Declare @MasterClient int,
          @ConsolClient int

  Select @MasterClient = 1, @ConsolClient = 2  


Select * from #ProductSub t1
  /* Use Master Client ID When Expiry Date is Null) */
  Where (ClientID = @MasterClient and ExpiryDate is null)
  /* Use Consol ClientID if Expiry Date is null nut Expiry Date for Master Client ID is not */
  OR    (ClientID = @ConsolClient and ExpiryDate is null and ProductID not in (
            Select ProductID from #ProductSub t2
            Where (ClientID = @MasterClient and ExpiryDate is null))
        ) 
  OR   -- OH NO my head exploded
/*  OR EXISTS (Select 1
             from #ProductSub t3
            )*/

Drop Table #ProductSub   

/**********  Expected  Output  ************************
ClientID     ProductID     ExpiryDate
1            100           NULL
1            101           NULL
2            102           NULL
1            200           NULL
2            300           NULL
1            400           2009-01-01 00:00:00
2            500           2009-01-01 00:00:00
1            600           2009-01-01 00:00:00

任何和所有帮助都非常感谢

编辑：虽然听起来像这样，但这不是家庭作业，而是一个现实生活中的问题，我希望找到一个现实生活解决方案，我可以自己做这件事，但我所有的解决方案都通向临时表。需要指出的是，生产环境是SQLServer 7！

Answer 1

在这里，我已将条件移至子查询。子查询连接 Consol 和 Master 的行，因此您可以访问这两行中的列。条件仍然有点复杂，因为任何一行都可能丢失。

select ps.*
from @ProductSub ps
inner join (
    select     
      CASE 
        WHEN c.ClientID is null THEN m.ClientID
        WHEN m.ClientID is null THEN c.ClientID
        WHEN m.ExpiryDate is not null and c.ExpiryDate is not null THEN
          CASE 
            WHEN c.ExpiryDate > m.ExpiryDate THEN c.ClientID
            ELSE m.ClientID
          END
        WHEN m.ExpiryDate is null THEN m.ClientID
        WHEN c.ExpiryDate is null THEN c.ClientID
        ELSE m.ClientID
      END as ClientId,
      COALESCE(m.ProductId, c.ProductId) as ProductId
    from       @ProductSub m
    full outer join  @ProductSub c
    on         m.ProductID = c.ProductID
    and        m.ClientID <> c.ClientID
    where      IsNull(m.clientid,@MasterClient) = @MasterClient
    and        IsNull(c.clientid,@ConsolClient) = @ConsolClient
) filter
on filter.clientid = ps.clientid
and filter.productid = ps.productid
order by ps.ProductId

Answer 2

问题尚不清楚，但据我解释，可能是这样的：

DECLARE @MasterExpiry smalldatetime, @ConsolExpiry smalldatetime
SELECT @MasterExpiry = ExpiryDate FROM #ProductSub WHERE ClientID = @MasterClient
SELECT @ConsolExpiry = ExpiryDate FROM #ProductSub WHERE ClientID = @ConsolClient

SELECT CASE
    WHEN @MasterExpiry IS NULL AND @ConsolExpiry IS NULL THEN @MasterClient
    WHEN @MasterExpiry IS NULL THEN @MasterClient
    WHEN @ConsolExpiry IS NULL THEN @ConsolClient
    WHEN @MasterExpiry >= @ConsolExpiry THEN @MasterClient
    ELSE @ConsolClient END AS [Client]

如果您需要行数据，则将其选择到变量中并执行单独的 SELECT 操作？

DECLARE @FinalClient int
SELECT @FinalClient = CASE
    WHEN @MasterExpiry IS NULL AND @ConsolExpiry IS NULL THEN @MasterClient
    WHEN @MasterExpiry IS NULL THEN @MasterClient
    WHEN @ConsolExpiry IS NULL THEN @ConsolClient
    WHEN @MasterExpiry >= @ConsolExpiry THEN @MasterClient
    ELSE @ConsolClient END

SELECT * FROM #ProductSub WHERE ClientID = @FinalClient