sql server2008 จะกำหนด id เป็น pk โดยที่มี 4 หลัก เริ่มจาก 0001...

declare @LastId int
set @LastId = (select isnull(max(cast(Id as int)), 0) + 1 from TblId)
select replicate('0', 4 - len(@LastId)) + cast(@LastId as varchar) as Id

   string sqlNewID;
            sqlNewID  = " SELECT    * ";
            sqlNewID += " FROM      Sale";

            SqlDataReader dr;
            com = new SqlCommand();
            com.CommandType = CommandType.Text;
            com.CommandText = sqlNewID;
            com.Connection = Conn;
            dr = com.ExecuteReader();
            if (dr.HasRows)
            {
                DataTable dtNewID = new DataTable();
                dtNewID.Load(dr);

    string ID;
    int ReciveID;


ID      = dtNewID.Rows[0]["SaleID"].ToString();
ReciveID       = 10001 + Convert.ToInt32(SQLSaleID.Substring(1, 4));
txtSaleID.Text = ReciveID.ToString();  

 }
            else
            {
                txtSaleID.Text =0001;            
}
            dr.Close();