How to get data from a column by selecting column name in firebird

[satti]

In sql server we use schema but iwant to know that how we get data from a specific column by selecting its column name.
there is a combo box that contain column names , now i want that when we select column name in combo it show the data of that column .
my combo code for getting columns from firebird db is

Private Sub txt1_GotFocus(ByVal sender As Object, ByVal e As System.EventArgs) Handles txt1.GotFocus
        Try
            txt1.Items.Clear()
            myRead.myfill("select *  from rdb$relation_fields f where f.rdb$relation_name = 'TB_OBV'")
            Dim rc, lr As Integer
            lr = myRead.dt.Columns.Count - 1
            For rc = 0 To lr
                txt1.Items.Add(myRead.dt.Rows(rc).Item(0))

            Next
        Catch exc As Exception
            Exit Sub
        End Try
    End Sub