Why SQL statement was run twice

Hi All,
I am a newbie in ASP, and I'm trying to fix a problem in an old system that I'm supporting.
The problem is that sometimes, one particular insert statement is run twice,
so I will have 2 duplicate records
inserted. I have checked and made sure that
the form is only submitted once.
This problem does not happen all the time.
And in the profiler, when it happened, I can see that the
insert statement was run twice consecutively.

Below is a snippet of the code:

Dim strSQL, strID
Dim objConnection, objRS
Set objConnection = oGetADOConnection(strConnectionString) 	
Dim strUserName 	

Set objRS = objConnection.Execute("SELECT UserName FROM Member WHERE UserID = '" & userID & "')"
		
If Not objRS.EOF Then
	wData = objRS.GetRows
	strUserName = wData(0,0)
End If	
Set objRS = Nothing

If strUserName <> "" Then	
            'this statement run twice			
	strSQL = "IF NOT EXISTS " & _
		  "(SELECT * from Card " & _
		  "WHERE CardNo = '" & strCardNo & "' ) " & _
		  "INSERT INTO Card (CardNo, UserName) " & _
		  "VALUES("'" & strCardNo & "','" & strUserName & "')"  
					
	Set objRs = objConnection.Execute(strSQL)
	Set objRs = Nothing
			
	strSQL = "SELECT @@IDENTITY as Value"
	Set objRs = objConnection.Execute(strSQL) 
					
	wData = objRs.GetRows	
			
	strID = cstr(wData(0,0))
		
	Set objRs = Nothing	
End If	
Set objConnection = Nothing

Code (markup):

Does anyone know what cause this problem and how
can I fix it?

Thank you

 

It needs to be done in a transaction to prevent a race condition.

 

Hi plb. Thank you for your reply.
I'm not really sure what that means, but I'll check it out