Question

我有一个问题，我试图获取每个折扣的百分比值，但复杂的部分是有两种类型的折扣。灵活折扣和固定折扣。我试图获取所有折扣的百分比，具体取决于折扣的类型，例如修复了我进入固定折扣表并从FlexiBand折扣表中检索百分比的百分比。

我的表及其属性：

Discount:
DiscountID,
Name,
Type

FixedDiscount:
DiscountID,
Percentage

FlexibleDiscount:
DiscountID

FlexiBand:
UpperBound,
PercentageRate,
DiscountID

我收到错误java.sql.SQLException: Column 'PercentageRate' not found.

当我这样做时：

 public ArrayList<Discount> getDiscounts() throws SQLException {

    Connection con = null;
    PreparedStatement stmt = null;
    ResultSet rs = null;

    ArrayList<Discount> discount = new ArrayList<Discount>();

    con = DriverManager.getConnection("jdbc:mysql://localhost:3306/abpp034?user=abpp034&password=120001772");

    stmt = con.prepareStatement("SELECT Discount.DiscountID, Discount.Type, FixedDiscount.Percentage\n" +
"FROM Discount\n" +
"INNER JOIN FixedDiscount\n" +
"ON Discount.DiscountID = FixedDiscount.DiscountID\n" +
"\n" +
"UNION\n" +
"\n" +
"SELECT Discount.DiscountID, Discount.Type, FlexiBand.PercentageRate\n" +
"FROM Discount\n" +
"INNER JOIN FlexiBand\n" +
"ON Discount.DiscountID = FlexiBand.DiscountID");


    try {

        while (rs.next()) {

            Discount d = new Discount();
            Fixed_Discount fd = new Fixed_Discount();
            FlexiBand fb = new FlexiBand();                
            d.setDiscountId(rs.getInt("DiscountID"));
            d.setType(rs.getString("Type"));      
            fd.setPercentage(rs.getInt("Percentage"));
            fb.setPercentageRate(rs.getInt("PercentageRate"));



            discount.add(d);
            discount.add(fd);
            discount.add(fb);

        }

        } finally {

        if (rs != null) {
            try {
                rs.close();
            } catch (SQLException se) {
                System.out.println(se.getErrorCode());
            }
        }
        if (stmt != null) {
            try {
                stmt.close();
            } catch (SQLException se) {
                System.out.println(se.getErrorCode());
            }
        }
        if (con != null) {
            try {
                con.close();
            } catch (SQLException se) {
                System.out.println(se.getErrorCode());
            }
        }
    }

    return discount;

    }

奇怪的是，PercentageRate确实存在于FlexiBand表中，但我认为问题出在UNION之后，下一个语句没有被正确识别。

Answer 1

您可能希望从连接字符串中删除用户名和密码信息。独立运行时，两个查询都会干净地启动吗？你的RDBMS是mysql还是sql-server？

使用UNION从结果集中获取各个表的列值

1 个答案: