Discuss "Concatenation of Column Data function" in the Microsoft Access forum.

Public Function Conc(Fieldx, Identity, Value, Source) As Variant
  Dim cnn As ADODB.Connection
  Dim rs As ADODB.Recordset
  Dim SQL As String
  Dim vFld As Variant
  
  Set cnn = CurrentProject.Connection
  Set rs = New ADODB.Recordset
  vFld = Null
  
  SQL = "SELECT [" & Fieldx & "] as Fld" & _
        " FROM [" & Source & "]" & _
        " WHERE [" & Identity & "]='" & Value & "'"
  
  ' open recordset.
  rs.Open SQL, cnn, adOpenForwardOnly, adLockReadOnly
  
  ' concatenate the field.
  Do While Not rs.EOF
    If Not IsNull(rs!Fld) Then
      vFld = vFld & ", " & rs!Fld
    End If
    rs.MoveNext
  Loop
  ' remove leading comma and space.
  vFld = Mid(vFld, 3)
  
  Set cnn = Nothing
  Set rs = Nothing
  
  ' return concatenated string.
  Conc = vFld
End Function

SELECT Conc("ConcatField","Byfield",[Byfield],"Table/Query") AS Field
FROM Table/Query;