How to get value in comboboxcolumn of datagridview from database

I have 3 comboboxcolumn in datagridview.I want to display its value in grid if its value in database table is not null.Eg one column is caste.if this is null in my databse table then combobox column should be added to grid else caste value shold be seen in combobox when datagridview loads..Can any1 help me.
Below is my code:

Dim cast As Integer = 0
            Dim con As OdbcConnection = New OdbcConnection
            sql = "Select d.caste from datafile d where d.AC_NO = " & cmbVidhanNo.Text & " " + searchstring
            If rs.State = 1 Then rs.Close()
            rs.Open(sql, MainCon, 1, 3)
            Do While Not rs.EOF
                If Not IsDBNull(rs.Fields(0).Value) Then
                    cast = rs.Fields(0).Value
                End If
                If Not IsDBNull(cast) Then
                    With col_Caste
                        .Name = "Caste"
                        .HeaderText = "Caste"
                        .DataPropertyName = cast
                        .ReadOnly = False
                    End With
    
                Else
                    sql = "Select Desc from Category where Catgry = 1"
                    con.ConnectionString = connstring
                    If con.State = ConnectionState.Open Then con.Close()
                    con.Open()
                    Dim da As OdbcDataAdapter = New OdbcDataAdapter(sql, con)
                    da.Fill(ds, "Caste")
    
                    With col_Caste
                        .Name = "Caste"
                        .HeaderText = "Caste"
                        .DataSource = ds.Tables("Caste")
                        .DisplayMember = "Desc"
                        .ReadOnly = False
                    End With
    
                End If
                rs.MoveNext()
            Loop
    
            dgvUserDetails.Columns.Add(col_Caste)