Invalid Use of Null - Track Log On in Microsoft Access


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Invalid Use of Null

Rusty Abernathy

2 years ago

I am trying to incorporate the Tracking Logon/Log off into a school routine I am working on. I keep getting invalid use of null when anyone has the main menu open. If I close all main menus, the two query's work perfectly. If I remove the sort on the LogOnTime:TimeStamp in Query1 and leave the "Is Not Null" in LogOffTime: CDate(DMin("TimeStamp","LogT","(Event = ""Log Off"" or Event = ""Log On"") AND TimeStamp > #" & [TimeStamp] & "# AND Username = """ & [Username] & """")) Query 1 will work with the main menu loaded and the result matches logon/logoff just like it is supposed to. However, Query 2 still gets the "Invalid Use of Null" and I am sending query 1 as the source of Query 2.

Before I post all code can you confirm that Query 1 and Query 2 will work with a log on and no corresponding Log off. - Basically, asking if the queries should work with current log Ons.

Rusty Abernathy OP @Reply

2 years ago

I let AI produce code for this routine, and it works perfectly. I get, and wanted, a blank Log Off field for those currently logged on and I do not get any Invalid Use of Null errors. I would have never been able to come up with this solution, but AI did. The aggerate query works also. Both queries work regardless of if a user is currently logged in or not. Here are the entries for LogOffTime and Total minutes:

LogOffTime: (SELECT TOP 1 TimeStamp FROM LogT AS L2 WHERE L2.Username = LogT.Username AND L2.TimeStamp > LogT.TimeStamp ORDER BY TimeStamp)

TotalMinutes: DateDiff('n',[LogT].[TimeStamp],(SELECT TOP 1 TimeStamp FROM LogT AS L2 WHERE L2.Username = LogT.Username AND L2.TimeStamp > LogT.TimeStamp ORDER BY TimeStamp))

	Rusty Abernathy OP @Reply 2 years ago
Another nice thing is that I can put a button to click and see who is currently logged onto the database by using a very simple query:SELECT LogOnQ.Username, LogOnQ.LogOnTime FROM LogOnQ WHERE (((LogOnQ.LogOffTime) Is Null));

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