Question

I have a table called tblAssetsInUse with the following structure:

intPK      intAssetID      datCheckedOut     datCheckedIn 1          450             1/5/2009          10/5/2009 2          300             2/5/2009          <NULL> 3          200             2/5/2009          <NULL> 4          450             12/5/2009         5/7/2009 

and I have a SP that receives a scanned Asset ID then either Inserts, or Updates to the table for assets being checked Out or In respectively. As you can see datCheckedIn may be Null which is used to work out which assets are currently in use. This procedure works perfectly. I wish to be able to determine what the last asset to be scanned was and also what the last operation to the table was (i.e. Check In or Out). I have some SQL code which finds the row with the most recent date (regardless of which column) and I then use this to join to a separate Assets View, which also works. I just need to be able to work out if the most recent date was in the Checked Out or Checked In column somehow.

SELECT TOP (1) allDates.intPK, MAX(allDates.datLastAction) AS datLastScan,    dbo.viwAssets.strFriendlyName, tblAssetsInUse_join.intAssetID FROM (SELECT intPK, MAX(datCheckedOut) AS datLastAction       FROM dbo.tblAssetsInUse AS tblAssetsInUse_out       GROUP BY intPK        UNION ALL        SELECT intPK, MAX(datCheckedIn) AS datLastAction       FROM dbo.tblAssetsInUse AS tblAssetsInUse_in       GROUP BY intPK) AS allDates  INNER JOIN dbo.tblAssetsInUse AS tblAssetsInUse_join ON allDates.intPK = tblAssetsInUse_join.intPK  INNER JOIN dbo.viwAssets ON tblAssetsInUse_join.intAssetID = dbo.viwAssets.intPK GROUP BY allDates.intPK, dbo.viwAssets.strFriendlyName, tblAssetsInUse_join.intAssetID ORDER BY datLastScan DESC 

Is there a literal value of some kind I can add in so that it flags a bit value in the results perhaps?

Thanks for your help,

Paul Reynolds

Answer 1

Beside from getting the type of operation performed, I think that the whole query could be simplified (and optimized) this way:

SELECT TOP 1 allDates.intPK, allDates.datLastAction AS datLastScan, allDates.operation, dbo.viwAssets.strFriendlyName, tblAssetsInUse_join.intAssetID FROM (SELECT TOP 1 intPK, intAssetID, datCheckedOut AS datLastAction, 'Out' AS operation   FROM dbo.tblAssetsInUse AS tblAssetsInUse_out   ORDER BY datCheckedOut DESC    UNION ALL    SELECT TOP 1 intPK, intAssetID, datCheckedIn AS datLastAction, 'In' AS operation   FROM dbo.tblAssetsInUse AS tblAssetsInUse_in   ORDER BY datCheckedIn DESC) AS allDates  INNER JOIN   dbo.viwAssets ON allDates.intAssetID = dbo.viwAssets.intPK ORDER BY datLastScan DESC 

EDIT: also note that by removing the TOP 1 in the first line you get both the last Asset checked in and the last checked out.