protected void Bind()
    {
        DataTable dt = AddSQLStringToDAL.GetDistinctColums("TabTeachers", "Department");

        for (int i = 0; i < dt.Rows.Count; i++)
        {
            ddlDepartment.Items.Add(dt.Rows[i][0].ToString());
        }

        DataTable dt1 = AddSQLStringToDAL.GetDistinctColums("TabTeachers", "Role");

        for (int i = 0; i < dt1.Rows.Count; i++)
        {
            ddlRole.Items.Add(dt1.Rows[i][0].ToString());
        }

        DataTable dt2 = AddSQLStringToDAL.GetDistinctColums("TabTeachers", "Type");

        for (int i = 0; i < dt2.Rows.Count; i++)
        {
            ddlTeachersType.Items.Add(dt2.Rows[i][0].ToString());
        }
    }