sSQL = "SELECT * FROM BRIEFE WHERE BRIEFNUMMER='4711'"
dbcmd.CommandText = sSQL
Dim ds As DataSet = New DataSet()
Dim da As FbDataAdapter = New FbDataAdapter(sSQL, dbcon)
da.Fill(ds, "BRIEFE")
Dim myDataRelation1 As DataRelation
myDataRelation1 = New DataRelation("TEST", ds.Tables("BRIEFE").Columns( _
  "BRIEFNUMMER"), ds.Tables("SCHRIFTVERKEHR").Columns("BRIEFNUMMER"))
 
ds.Relations.Add(myDataRelation1)
DataGridView1.DataMember = "Test"
DataGridView1.DataSource = ds.Tables("BRIEFE")