Is it possible to create a recursive query in Access?

Question

I have a job table

Id
ParentID
jobName
jobStatus

The root ParentID is 0.

Is it possible in Access to create a query to

Answer 1

This cannot be done using pure SQL in Access, but a little VBA goes a long way.

Add a reference to the Microsoft Scripting Runtime (Tools -> References...).

This assumes that the ID is unique, and that there are no cycles: e.g. A's parent is B, but B's parent is A.

Dim dict As Scripting.Dictionary

Function JobRoot(ID As Long) As Long
    If dict Is Nothing Then
        Set dict = New Scripting.Dictionary
        Dim rs As DAO.Recordset
        Set rs = CurrentDb.OpenRecordset("SELECT ID, ParentID FROM Job", dbOpenForwardOnly, dbReadOnly)
        Do Until rs.EOF
            dict(rs!ID) = rs!ParentID
            rs.MoveNext
        Loop
        Set rs = Nothing

        Dim key As Variant
        For Each key In dict.Keys
            Dim possibleRoot As Integer
            possibleRoot = dict(key)
            Do While dict(possibleRoot) <> 0
                possibleRoot = dict(possibleRoot)
            Loop
            dict(key) = possibleRoot
        Next
    End If
    JobRoot = dict(ID)
End Function

Sub Reset() 'This needs to be called to refresh the data
    Set dict = Nothing
End Sub