Monday, 17 October 2011

OUTER APPLY

a good sample for OUTER APPLY:

Returning the latest record of a child table:

SELECT ST.[SystemDetailID], ST.[SystemName], LH.LatestLoadStatus
FROM [SystemTable] AS ST
LEFT OUTER JOIN
(
SELECT LHInner.LoadStatus AS LatestLoadStatus, LHInner.SystemDetailID FROM [dbo].[LoadHistory] AS LHInner
WHERE LHInner.LoadHistoryID in
(
SELECT LatestLoadHisotoryID FROM
(
SELECT MAX(LoadHistoryID) as LatestLoadHisotoryID, SystemDetailID FROM [dbo].[LoadHistory]
GROUP BY SystemDetailID
) l
)
) AS LH ON ST.SystemDetailID = LH.SystemDetailID


A simpler/shorter approach is:



SELECT ST.[SystemDetailID],
ST.[SystemName],
LH.LatestLoadStatus
FROM [SystemTable] AS ST
OUTER APPLY (SELECT TOP 1 *
FROM [dbo].[LoadHistory] LH
WHERE ST.SystemDetailID = LH.SystemDetailID
ORDER BY LoadHistoryID DESC) LH



More info: http://technet.microsoft.com/en-us/library/ms175156.aspx

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