java - SQL 错误 (java.sql.SQLException)

Question

我在 Java 中得到了这两个表单，它们链接到 MySQL 中的两个表。我已经完成连接，数据库保存通过前端输入的数据。但这两种形式是相互联系的。就像当在一个表单中单击一个按钮时，它会将所有数据以表格的形式发送到另一个表单。这是我为此所做的编码:

int dress1=100;
double price1=Double.parseDouble(Price1.getText());
DefaultTableModel CurrentPurchases= new DefaultTableModel();
int rows=CurrentPurchases.getRowCount();
if (rows>0){
    for (int i = 0; i < rows; i++) {
    CurrentPurchases.removeRow(0); }
}
try{
    Connection connection=getConnection();
    stmt=connection.createStatement();
    String Buy1Query1="Update Products set Quantity=Quantity-1 where Product_no=1;";
    String Buy1Query2="Insert into Buy values('"+Pname1.getText()+"',"+price1+");";
    stmt.executeUpdate(Buy1Query1);
    stmt.executeUpdate(Buy1Query2);
    dress1--;
    if(dress1==0){
        JOptionPane.showMessageDialog(null,"Sorry, This Item is Out of Stock!");
    }
    new ShoppingCart().setVisible(true);
    String Pname="";
    double Price;
    PreparedStatement buyquery=connection.prepareStatement("Select * from Buy;");
    rs=buyquery.executeQuery();
    Pname=rs.getString("ProductName");
    Price=rs.getDouble("Price");
    CurrentPurchases.addRow(new Object[]{Pname,Price});

}
catch(SQLException ex){
    ex.printStackTrace();
    ex.getErrorCode();
}
finally{}

当我运行该文件时，出现以下错误:

java.sql.SQLException
        at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1055)
        at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:956)
        at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:926)
        at com.mysql.jdbc.ResultSetImpl.checkRowPos(ResultSetImpl.java:815)
        at com.mysql.jdbc.ResultSetImpl.getStringInternal(ResultSetImpl.java:5528)
        at com.mysql.jdbc.ResultSetImpl.getString(ResultSetImpl.java:5448)
        at com.mysql.jdbc.ResultSetImpl.getString(ResultSetImpl.java:5488)
        at Fashion_Footwear.Buy1ActionPerformed(Fashion_Footwear.java:370)
        at Fashion_Footwear.access$000(Fashion_Footwear.java:19)
        at Fashion_Footwear$1.actionPerformed(Fashion_Footwear.java:100)
        at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
        at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
        at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
        at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
        at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
        at java.awt.Component.processMouseEvent(Component.java:6216)
        at javax.swing.JComponent.processMouseEvent(JComponent.java:3265)
        at java.awt.Component.processEvent(Component.java:5981)
        at java.awt.Container.processEvent(Container.java:2041)
        at java.awt.Component.dispatchEventImpl(Component.java:4583)
        at java.awt.Container.dispatchEventImpl(Container.java:2099)
        at java.awt.Component.dispatchEvent(Component.java:4413)
        at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4556)
        at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4220)
        at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4150)
        at java.awt.Container.dispatchEventImpl(Container.java:2085)
        at java.awt.Window.dispatchEventImpl(Window.java:2475)
        at java.awt.Component.dispatchEvent(Component.java:4413)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

当我点击此错误时:

 at Fashion_Footwear.Buy1ActionPerformed(Fashion_Footwear.java:370)

它给了我这个错误代码:

    Pname=rs.getString("ProductName");

我是这一切的新手，如果有人尽快帮助我，我将非常感激。先感谢您!

表购买:

create table buy(ProductName varchar(100),Price decimal(7,2));

Answer 1

问题是您的ResultSet位于第一行之前。您应该使用如下代码:

PreparedStatement buyquery=connection.prepareStatement("Select * from Buy;");
rs=buyquery.executeQuery();
if (rs.next())
{
    Pname=rs.getString("ProductName");
}