Viewing a Nested Set Model tree as an Adjacency List

Recently, I needed to view a Nested Set Model tree as an Adjacency list so I could use it with VB's TreeCtrl.

Here's the MS-SQL view I came up with:

SELECT   T1.irpCategory, T1.iwmleft, T1.iwmright, T1.swmCategoryName, T1.ircDepth, T2.ircParentID
FROM     (SELECT   TOP 100 PERCENT node.irpCategory, node.iwmleft, node.iwmright, node.swmCategoryName, (COUNT(parent.swmCategoryName) - 1) 
                       AS ircDepth
            FROM     dbo.tblCategories AS node, dbo.tblCategories AS parent
            WHERE   node.iwmleft BETWEEN parent.iwmleft AND parent.iwmright
            GROUP BY node.irpCategory, node.swmCategoryName, node.iwmleft, node.iwmright
            ORDER BY node.iwmleft) T1 LEFT OUTER JOIN
             (SELECT   TOP 100 PERCENT irpCategory,
                            (SELECT   TOP 1 irpCategory
                             FROM     dbo.tblCategories t2
                             WHERE   t2.iwmleft < t1.iwmleft AND t2.iwmright > t1.iwmright
                             ORDER BY t2.iwmright - t1.iwmright ASC) AS ircParentID
              FROM     dbo.tblCategories t1
              ORDER BY iwmright - iwmleft DESC) T2 ON T1.irpCategory = T2.irpCategory

And the VB for the TreeCtrl object called tvCategories:

Private Sub Refresh_tvCategories()
On Error GoTo Err_Handler
Dim vNodeSet As Variant
Dim db As DAO.Database
Dim rs As DAO.Recordset
Dim bFirstItem As Boolean
Dim sFirstKey As String
    Set db = CurrentDb
    'SQLCategoriesList is a odbc passthru query to the view on the MSSQL server
    Set rs = db.OpenRecordset("SELECT * FROM SQLCategoriesList")
    bFirstItem = True
    
    
    If Not rs.EOF Then
        rs.MoveFirst
        While Not rs.EOF
                        

            If IsNull(rs.Fields("ircParentID")) Then
                Set vNodeSet = tvCategories.Nodes.Add()
                vNodeSet.Key = "K" & rs.Fields("irpCategory")
                vNodeSet.Expanded = False
                vNodeSet.Text = rs.Fields("swmCategoryName")
            Else
                'Tree Controls need text for their IDs so I'm prefixing the ID numbers with the letter K
                Set vNodeSet = tvCategories.Nodes.Add("K" & rs.Fields("ircParentID"), tvwChild)
                vNodeSet.Key = "K" & rs.Fields("irpCategory")
                vNodeSet.Expanded = False
                vNodeSet.Text = rs.Fields("swmCategoryName")
            End If
            If bFirstItem Then
                sFirstKey = vNodeSet.Key
                bFirstItem = False
            End If
            rs.MoveNext
        Wend
    End If
    
    'for some reason the form doesnt work properly unless an item has been selected at some point
    tvCategories.Nodes(sFirstKey).Selected = True
    'it can be unslected straight away
    
    
    
Exit_Err_Handler:
    Exit Sub
    
Err_Handler:
    Select Case Err.Number
       Case vbObjectError + 1
          Resume Next
       Case Else
          msgbox Err.Number & Err.Description
          Resume Exit_Err_Handler
    End Select

End Sub