违反并发性: UpdateCommand

这是加载,程序开始的时候加载dtAllQty表（在外的地方加载的）然后和dtqty这个表合并一下，
dtAllQty字段比dtqty多，去掉一些多余的字段，dtqty表和下面那句sql字段是一样的但是保存的时候总是提示
违反并发性: UpdateCommand 影响了预期 1 条记录中的 0 条。不知道为什么?
string sql = @"select top 1 monthy,processid,shiftid,empid,workqty,monthreward,qualityrate,jumprate,JumpReward,profitreward,addreward,buckqty,buckreward,realreward,persons,avgreward,judgtime from monthdonereward where 1=2";
                dtQty = SqlHelper.GetDataTable(sql);
                dtQty.Merge(dtAllQty, true, MissingSchemaAction.Ignore);
                dgview.DataSource = dtQty.DefaultView;
string sql = @"select monthy,processid,shiftid,empid,workqty,monthreward,qualityrate,jumprate,JumpReward,profitreward,addreward,buckqty,buckreward,realreward,persons,avgreward,judgtime from monthdonereward";
            try
            {
                SqlConnection con = new SqlConnection(Config.ConnectionString);
                SqlCommand cmd = new SqlCommand(sql, con);
                SqlDataAdapter ada = new SqlDataAdapter(cmd);
                SqlCommandBuilder build = new SqlCommandBuilder(ada);
                ada.Update(dtQty);