Question

I’m trying to write a VBA function that gets a value from an Access table using a SELECT query. Here’s the code:

Function getTableValue(uniqueID As Long, tableName As String, _ 
idField As String, tableField As String) As Variant

Dim db As Database
Dim rs As Recordset
Dim selectSQL As String

selectSQL = "select * from " & tableName & " where " & idField & "=" & uniqueID

Set db = OpenDatabase(dbPath)
Set rs = db.OpenRecordset(selectSQL)

If rs.RecordCount > 0 Then
    rs.MoveLast
    rs.MoveFirst
    getTableValue = rs.Fields(tableField)
End If

End Function

When the field specified by tableField is a Date/Time type and the field is empty, getTableValue() returns an “Invalid use of Null” error. I thought that having the function return a Variant would allow me to return Null values; what should I do to handle these empty dates?

Answer 1

It turns out that the function’s Null value was being passed to a Date/Time variable. I’ve fixed that by using the following:

dim myDate as date
dim myVar as variant

myVar=getTableValue(idNum,"thisTable","idField", "valueField")
if isNull(myVar) then
 myDate=0
else
 myDate=myVar
endif

While it doesn’t check whether or not myVar returns a Date, valueField‘s values are of type Date/Time so it’s ok.