Question

下面的代码我没有异常错误，这可能意味着我的sql语句没有问题。但是，在尝试验证它是否返回任何值时，我将返回的项目传递给字符串值并尝试在消息框中显示它。

我面临的问题是消息框只显示列的名称，而不是表格中请求的数据。

可能是什么问题？如果有更好的解决方法，请提出建议......

    public void DisplayPurchase(OleDbConnection mDB)
    {
        openDB();
        string sqlQuery;
        OleDbCommand cmd;
        OleDbDataReader rdr;



        sqlQuery = "SELECT CustomerTable.[Youth ID], CustomerTable.Firstname, " +
            "CustomerTable.Lastname, Youth.Purchaseid, Youth.NumbersOfSport, " + 
            "Youth.Price, Youth.TotalCostOfTraining, Youth.PercentageDiscount, " +
            "Youth.AmountDue, Youth.DatePurchased" +
            " FROM CustomerTable, Youth WHERE Youth.YouthID = CustomerTable.[Youth ID]" +
            " AND CustomerTable.[Youth ID] = 7";

        try
        {
            cmd = new OleDbCommand(sqlQuery, mDB);

            rdr = cmd.ExecuteReader();
            if (rdr.HasRows)
            {
                qtyInt1 = (int)rdr["Youth.NumbersOfSport"];
                youthInt1 = (int)rdr["CustomerTable.[Youth ID]"];
                firstStr1 = (string)rdr["CustomerTable.Firstname"];
                purStr1 = (string)rdr["Youth.Purchaseid"];
                lastStr1 = (string)rdr["CustomerTable.Lastname"];
                priceStr1 = (string)rdr["Youth.Price"];
                totalCstStr1 = (string)rdr["Youth.TotalCostOfTraining"];
                discountStr1 = (string)rdr["Youth.PercentageDiscount"];
                amtDueStr1 = (string)rdr["Youth.AmountDue"];
                //purDate1 = (DateTime)rdr["Youth.DatePurchased"];

                MessageBox.Show(firstStr1.ToString());

                closeDB();

            }
            else
            {
                MessageBox.Show("Reader has no rows");
                closeDB();
            }
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
        }


    }

谢谢

Answer 1

我很确定你必须先调用rdr.Read（）才能访问它的任何数据。因此，将其添加为if之后的第一行（rdr.HasRows（））

Answer 2

您需要在阅读器上调用Read（）以读取第一行。

if(rdr.HasRows) {
    rdr.Read();
    ...

祝你好运，
费边

Answer 3

你试过了吗？

firstStr1 = (string)rdr["Firstname"];

datareader中的字段名称通常不包含表名前缀。

Answer 4

检索数据时删除表名：

qtyInt1 = (int)rdr["NumbersOfSport"];
youthInt1 = (int)rdr["Youth ID"];  // You may need to rename this one in the query
firstStr1 = (string)rdr["Firstname"];
purStr1 = (string)rdr["Purchaseid"];
lastStr1 = (string)rdr["Lastname"];
priceStr1 = (string)rdr["Price"];
totalCstStr1 = (string)rdr["TotalCostOfTraining"];
discountStr1 = (string)rdr["PercentageDiscount"];
amtDueStr1 = (string)rdr["AmountDue"];

Answer 5

令人惊讶的是这些东西的运作方式...... 我首先要感谢所有为解决这个问题做出贡献的人。非常感谢所发布的每一个字母。

sqlQuery =“SELECT Youth.YouthID，Firstname，Lastname，NumbersOfSport，Price，TotalCostOFTraining，PercentageDiscount，Purchaseid，AmountDue，DatePurchased FROM CustomerTable，Youth WHERE CustomerTable.YouthID = Youth.YouthID AND Youth.YouthID =”+ toSql（youthInt））;

        try
        {
            cmd = new OleDbCommand(sqlQuery, mDB);

            rdr = cmd.ExecuteReader();
            if (rdr.HasRows)
            {
                rdr.Read();
                qtyInt1 = (int)rdr["NumbersOfSport"];
                youthInt1 = (int)rdr["YouthID"];
                firstStr1 = (string)rdr["Firstname"];
                purInt1 = (int)rdr["Purchaseid"];
                lastStr1 = (string)rdr["Lastname"];
                priceStr1 = (string)rdr["Price"];
                totalCstStr1 = (string)rdr["TotalCostOfTraining"];
                discountStr1 = (string)rdr["PercentageDiscount"];
                amtDueStr1 = (string)rdr["AmountDue"];
                purDate1 = (DateTime)rdr["DatePurchased"];



                closeDB();

            }
            else
            {
                MessageBox.Show("Reader has no rows");
                closeDB();
            }
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
        }


    }

我不得不打电话给rdr.read（）;函数以及引用数据库列的表，每个帮助来自不同的来源..... 棒极了... 谢谢大家...

从OleDb查询中检索数据不在MessageBox中显示

5 个答案: