访问2010 sql以选择两个记录之一

Question

I am pretty sure I have to use an IIF statement but I'm not sure how to implement it in this scenario...

I am writing a query to check user IDs from one place against a master record set. However in some cases the criteria that I am using to obtain the User ID from the master record set sometimes links to more than one User ID. One is to a user ID of people that have been deleted and one is to a user that is active. In the case that there is two records returned, I need my query to select the active person instead of the deleted person...

Here is my query so far

INSERT INTO VExceptions ( Carrier, [Wireless Number], Period,    Carrier_UserName,     Carrier_UserID, Parsed_PersNo_Carrier, MT_UserID,     MT_Cost_Center, MT_Status, [CountOfUser ID], IsSpare )
SELECT LoadFile_VCharges.Carrier, LoadFile_VCharges.[Wireless Number],     LoadFile_VCharges.Period, LoadFile_VCharges.[User Name],     LoadFile_VCharges.[User ID], LoadFile_VCharges.[Personnel Number],     MT.UserID, MT.CostCenter, MT.Status, Count(MT.UserID) AS CountOfUserID,     IIf(InStr(1,[User Name],"SPARE")>0,1,0) AS IsSpare
FROM LoadFile_VCharges LEFT JOIN MT ON LoadFile_VCharges.[Personnel Number]     = MT.PersonnelNumber
GROUP BY LoadFile_VCharges.Carrier, LoadFile_VCharges.[Wireless Number],     LoadFile_VCharges.Period, LoadFile_VCharges.[User Name],     LoadFile_VCharges.[User ID], LoadFile_VCharges.[Personnel Number],     MT.UserID, MT.CostCenter, MT.Status, IIf(InStr(1,[User Name],"SPARE")>0,1,0)
HAVING (((LoadFile_VCharges.[User ID])="NA" Or (LoadFile_VCharges.[User ID])<>    [MT].[UserID]))
ORDER BY LoadFile_VCharges.[Wireless Number];

Aside from sometimes selecting the wrong record, this query works fine...

Any suggestions would be greatly appreciated.

Regards,

AG

Answer 1

One strategy is to left join on two subqueries, one for the active set and one for inactive set. Then in the select clause select the first option that is not null. You can do that with COALESC, CASE, or Nz. I think Access 2010 uses Nz. What Nz(active.UserID, inactive.UserID) says is "Use active.UserID if it exists, if it's null then use inactive.UserID."

SELECT LoadFile_VCharges.Carrier
    , LoadFile_VCharges.[Wireless Number]
    , LoadFile_VCharges.Period
    , LoadFile_VCharges.[User Name]
    , LoadFile_VCharges.[User ID]
    , LoadFile_VCharges.[Personnel Number]
    , Nz(active.UserID, inactive.UserID)
    , Nz(active.CostCenter, inactive.CostCenter)
    , Nz(active.Status, inactive.Status)
    , Count(LoadFile_VCharges.[User ID]) AS CountOfUserID
    , IIf(InStr(1,[User Name],"SPARE")>0,1,0) AS IsSpare

FROM LoadFile_VCharges 
    LEFT JOIN (SELECT UserID, CostCenter, Status FROM MT WHERE Status = 'Active') active ON (LoadFile_VCharges.[Personnel Number] = active.PersonnelNumber) 
    LEFT JOIN (SELECT UserID, CostCenter, Status FROM MT WHERE Status = 'Deleted') inactive ON (LoadFile_VCharges.[Personnel Number] = inactive.PersonnelNumber) 


GROUP BY LoadFile_VCharges.Carrier
    , LoadFile_VCharges.[Wireless Number]
    , LoadFile_VCharges.Period
    , LoadFile_VCharges.[User Name]
    , LoadFile_VCharges.[User ID]
    , LoadFile_VCharges.[Personnel Number]
    , MT.UserID, MT.CostCenter
    , MT.Status
    , IIf(InStr(1,[User Name],"SPARE")>0,1,0)

HAVING (((LoadFile_VCharges.[User ID])="NA" Or (LoadFile_VCharges.[User ID])<>[MT].[UserID]))

ORDER BY LoadFile_VCharges.[Wireless Number];

You may need to fiddle with the syntax. You might only need to Nz on the UserID column, I'm not sure. I'm sure there are other ways of doing it. I'm trying to think of a join where you get then entire active set (full join) and only the inactive set that does NOT overlap the active set (outer join). In MS SQL (non-Access) I would use a windowing function, but I don't think that doesn't exists in Access.