Is there a way to pivot a customer ID and a their

问题:

I have a query that gives me all customer's and their last three order dates.

EX:

CustomerId DateOrdered
167 2006-09-16 01:25:38.060
167 2006-09-21 13:11:53.530
171 2006-08-31 15:19:22.543
171 2006-09-01 13:30:54.013
171 2006-09-01 13:34:36.483
178 2006-09-04 11:36:19.983
186 2006-09-05 12:50:27.153
186 2006-09-05 12:51:08.513

I want to know if there is a way for me to pivot it to display like this:

[CustomerId]    [Most Recent] [Middle] [Oldest]
'167'   '2006-09-21 13:11:53.530'   '2006-09-16 01:25:38.060'   'NULL'
'171'    '2006-09-01 13:34:36.483'   '2006-09-01 13:30:54.013'   '2006-08-31 15:19:22.543'
'178'   '2006-09-04 11:36:19.983'   NULL    NULL
'186'   '2006-09-05 12:51:08.513'   '2006-09-05 12:50:27.153'   NULL    

回答1:

;WITH YourQuery As
(
SELECT CustomerId, DateOrdered,
ROW_NUMBER() OVER (PARTITION BY CustomerId ORDER BY DateOrdered DESC) AS RN
FROM Orders
)
select [CustomerId],
MAX(CASE WHEN RN=1 THEN DateOrdered END) AS  [Most Recent] ,
MAX(CASE WHEN RN=2 THEN DateOrdered END) AS  [Middle] ,
MAX(CASE WHEN RN=3 THEN DateOrdered END) AS  [Oldest] 
FROM YourQuery
WHERE RN<=3
GROUP BY [CustomerId]

回答2:

Warning: Not Tested

I think you're looking for something like this. The specific joins and where clause may need some work, but basically your just joining the table back on itself to get one date each time.

SELECT C.CUSTOMERID, C.DATEORDERED, C2.DATEORDERED, C3.DATEORDERED
FROM CUSTOMER C
INNER JOIN CUSTOMER C2 ON C.CUSTOMERID = C2.CUSTOMERID
INNER JOIN CUSTOMER C3 ON C.CUSTOMERID = C3.CUSTOMERID
WHERE C.DATEORDERED = MAX(C.DATEORDERED)
AND C2.DATEORDERED < C.DATEORDERED AND 
    (C3.DATEORDERED IS NULL OR C2.DATEORDERED >     C3.DATEORDERED)