这是关于northwind数据库查询的c#代码,无论怎么查,都是返回无结果,纳闷??????????那位高手帮妹妹查查看,先谢了

lstProducts.Items.Clear();
            //  here we go....
            // let's think about this.  what do we need to build the
            // correct sql string
            string sql = "SELECT * from  Products where 1=1 ";

            SqlConnection objconnection =
                  new SqlConnection(connection);
            SqlCommand objCommand = new SqlCommand();

            if (cboSearchCategory.SelectedIndex != -1)
            {
                Categories categ = new Categories ();
                categ = (Categories)cboSearchCategory.SelectedItem;
                sql += "and CategoryID=@categId ";
                objCommand.Parameters.AddWithValue("@categId",
                    categ.getCategoryId());
            }

            if (cboSearchSupplier .SelectedIndex !=-1)
            {
                // there's something selected in here
                // get it and and the appropriate where clause
                Suppliers supl = new Suppliers();
                supl = (Suppliers)cboSearchSupplier.SelectedItem;
                sql += " and SupplierID=@supId ";
                objCommand.Parameters.AddWithValue("@supId",
                    supl.getSupplierId());
            }

            if (chbSearchDiscontinued.Checked)
            {
                sql += " and Discontinued=1 ";
            }
            else if (!chbSearchDiscontinued.Checked)
            {
                sql += " and Discontinued=0 ";
            }

            objCommand.Connection = objconnection;
            objCommand.CommandText = sql;

            try
            {
                objconnection.Open();
                SqlDataReader reader =
                    objCommand.ExecuteReader();
                while (reader.Read())
                {
                    Products prod = new Products();
                    prod.setProductId(reader.GetInt32(0));
                    prod.setProductName(reader.GetString(1));
                    //prod.setQuantityPerUnit(reader.GetString(4));
                    //prod.setUnitPrice(reader.GetDecimal(5));
                    //prod.setUnitsInStock(reader.GetInt32(6));
                    //prod.setUnitsOnOrder(reader.GetInt32(7));
                    //prod.setReOrderLevel(reader.GetInt32(8));
                    //prod.setDisContinued(reader.GetBoolean(9));

                    lstProducts .Items.Add(prod);
                }
                if (lstProducts.Items.Count == 0)
                {
                    MessageBox.Show("There were no results to display for your query");
                }
            }
            catch (SqlException ex)
            {
                MessageBox.Show(ex.Message);
            }
            finally
            {
                objconnection.Close();
            } --------------------编程问答--------------------



            objCommand.Connection = objconnection; 

            objCommand.CommandText = sql;

你可以在我引用这段代码中加个断点调试看看，调试的时候注意观察下objCommand.CommandText的内容，并且将这个内容拷贝到查询分析其中运行下看出什么结果，是不是你预期的结果？不是的话估计就是你前面部分判断什么的弄的不对。 --------------------编程问答-------------------- 这类问题，调试就能解决了。。 --------------------编程问答-------------------- 老兄，像楼上所说，调试解决。

补充：.NET技术 ,  其他语言