如何确定客户历史记录的第一条记录中的单元格是否包含值？答案

【问题标题】：How do I determine whether a cell in the first record of a customers history contains a value?如何确定客户历史记录的第一条记录中的单元格是否包含值？
【发布时间】：2014-11-13 01:44:05
【问题描述】：

我有一个包含数年客户数据的门票表。我正在尝试确定访问过 x 次的客户在第一次访问时是否使用了优惠券。我有我正在使用的这个（下面的 SQL），以便我可以分解我正在寻找的组。关于这个群体，我真正想知道的是他们中有多少人在第一次访问时使用了优惠券（最早的 SaleDate）。

;WITH T AS
(
SELECT CustomerId, SaleDate, TotalCoupons,
       COUNT(*) OVER (PARTITION BY CustomerID) as Cnt
FROM    Store.dbo.Tickets
Where   (CreationDate between '2014-1-1' and '2014-11-12')
        and (IsDeleted = 0)
        And (TicketStatus = 'Complete')
)
SELECT CustomerID, SaleDate, TotalCoupons, Cnt                   
FROM T
WHERE Cnt = 10
order by CustomerId, SaleDate

作为最终结果，我只需要一个计数，不需要查看 CustomerID、SaleDate 等，我只需要一个（伪）Select Count(CustomerID)，其中 TotalCoupons 单元格上有一个值，它是最早的该 CustomerID 的记录。

我想我必须添加一个 RowID 并使用 Where RowID = 1 但我不确定如何将它用于我所做的事情。

【问题讨论】：

标签： sql sql-server-2008 common-table-expression

【解决方案1】：

可以使用row_number()判断第一次访问，然后使用条件聚合。以下获取带有标志的组中的客户：

WITH T AS (
      SELECT CustomerId, SaleDate, TotalCoupons,
             COUNT(*) OVER (PARTITION BY CustomerID) as Cnt,
             ROW_NUMBER() OVER (PARTITION BY CustomerID ORDER BY SaleDate) as seqnum
      FROM Store.dbo.Tickets
      Where (CreationDate between '2014-01-01' and '2014-11-12') and
            (IsDeleted = 0) and
            (TicketStatus = 'Complete')
     )
SELECT CustomerID, SaleDate, TotalCoupons, Cnt,
       MAX(CASE WHEN seqnum = 1 and TotalCoupons IS NOT NULL) as HasCouponFirstVisit              
FROM T
WHERE Cnt = 10;

您可以通过以下方式计算它们：

WITH T AS (
      SELECT CustomerId, SaleDate, TotalCoupons,
             COUNT(*) OVER (PARTITION BY CustomerID) as Cnt,
             ROW_NUMBER() OVER (PARTITION BY CustomerID ORDER BY SaleDate) as seqnum
      FROM Store.dbo.Tickets
      Where (CreationDate between '2014-01-01' and '2014-11-12') and
            (IsDeleted = 0) and
            (TicketStatus = 'Complete')
     )
SELECT COUNT(CustomerID)
FROM T
WHERE Cnt = 10 AND seqnum = 1 AND TotalCoupons IS NOT NULL;

我不确定TotalCoupons IS NOT NULL 是否正是您正在寻找的，但它应该足够接近。

【讨论】：