java.sql.SQLException：无效的游标状态：标识符游标未在UPDATE，DELETE，SET或GET语句中的行中定位： ResultSet为空

Question

我需要帮助来解决与使用HSQLDB从数据库提取数据相关的问题。 我得到错误：

java.sql.SQLException: invalid cursor state: identifier cursor not positioned on row in UPDATE, DELETE, SET, or GET statement: ; ResultSet is empty 
    at org.hsqldb.jdbc.JDBCUtil.sqlException(Unknown Source) 
    at org.hsqldb.jdbc.JDBCUtil.sqlException(Unknown Source) 
    at org.hsqldb.jdbc.JDBCUtil.sqlException(Unknown Source) 
    at org.hsqldb.jdbc.JDBCResultSet.getCurrent(Unknown Source) 
    at org.hsqldb.jdbc.JDBCResultSet.getColumnInType(Unknown Source) 
    at org.hsqldb.jdbc.JDBCResultSet.getString(Unknown Source) 
    at org.hsqldb.jdbc.JDBCResultSet.getString(Unknown Source) 
    at DBactionSearch.actionPerformed(DBactionSearch.java:109) 
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source) 
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source) 
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source) 
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source) 
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source) 
    at java.awt.Component.processMouseEvent(Unknown Source) 
    at javax.swing.JComponent.processMouseEvent(Unknown Source) 
    at java.awt.Component.processEvent(Unknown Source) 
    at java.awt.Container.processEvent(Unknown Source) 
    at java.awt.Component.dispatchEventImpl(Unknown Source) 
    at java.awt.Container.dispatchEventImpl(Unknown Source) 
    at java.awt.Component.dispatchEvent(Unknown Source) 
    at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source) 
    at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source) 
    at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source) 
    at java.awt.Container.dispatchEventImpl(Unknown Source) 
    at java.awt.Window.dispatchEventImpl(Unknown Source) 
    at java.awt.Component.dispatchEvent(Unknown Source) 
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source) 
    at java.awt.EventQueue.access$500(Unknown Source) 
    at java.awt.EventQueue$3.run(Unknown Source) 
    at java.awt.EventQueue$3.run(Unknown Source) 
    at java.security.AccessController.doPrivileged(Native Method) 
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source) 
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source) 
    at java.awt.EventQueue$4.run(Unknown Source) 
    at java.awt.EventQueue$4.run(Unknown Source) 
    at java.security.AccessController.doPrivileged(Native Method) 
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source) 
    at java.awt.EventQueue.dispatchEvent(Unknown Source) 
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source) 
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source) 
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source) 
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source) 
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source) 
    at java.awt.EventDispatchThread.run(Unknown Source) 
Caused by: org.hsqldb.HsqlException: invalid cursor state: identifier cursor not positioned on row in UPDATE, DELETE, SET, or GET statement: ; ResultSet is empty 
    at org.hsqldb.error.Error.error(Unknown Source) 
    at org.hsqldb.error.Error.error(Unknown Source) 
    at org.hsqldb.error.Error.error(Unknown Source) 
    ... 42 more 

的代码

有问题的部分是： text1 = rs.getString("firstname");

当我使用简单的SQL语句，比如SELECT firstname, middlename, lastname, emailaddress, phonenumber FROM MY_TABLE一切正常，但是当我使问题更加复杂在前面提到的部分WHERE (SELECT firstname, middlename, lastname, emailaddress, phonenumber FROM MY_TABLE WHERE '" + columnName + "' = '" + search + "'; ")添加变量出现错误。

这里是一流的全码：

import javax.swing.*; 
import java.awt.*; 
import java.awt.event.ActionEvent; 
import java.awt.event.ActionListener; 
import java.sql.Connection; 
import java.sql.DriverManager; 
import java.sql.ResultSet; 
import java.sql.Statement; 

public class DBactionSearch implements ActionListener { 

    JTextField textField1; 
    JTextField textField2; 
    JTextField textField3; 
    public JTextField textField4; 
    JTextField textField5; 
    JTextField textField6; 
    JTextArea textArea; 
    String text1; 
    String text2; 
    String text3; 
    String text4; 
    String text5; 
    String totalText; 
    JComboBox comboBox; 
    String search; 

    public void getTextField1(JTextField textField1) { 
     this.textField1 = textField1; 
    } 

    public void getTextField2(JTextField textField2) { 
     this.textField2 = textField2; 
    } 

    public void getTextField3(JTextField textField3) { 
     this.textField3 = textField3; 
    } 

    public void getTextField4(JTextField textField4) { 
     this.textField4 = textField4; 
    } 

    public void getTextField5(JTextField textField5) { 
     this.textField5 = textField5; 
    } 

    public void getTextField6(JTextField textField6) { 
     this.textField6 = textField6; 
    } 

    public void setTextArea(JTextArea textArea) { 
     this.textArea = textArea; 
    } 

    public void actionPerformed(ActionEvent e) { 

     String e1 = textField1.getText(); 
     String e2 = textField2.getText(); 
     String e3 = textField3.getText(); 
     String e4 = textField5.getText(); 
     String e5 = textField6.getText(); 
     final String columnName = textField4.getText(); 

     System.out.println("columnName = " + columnName); 

     switch (columnName) { 
     case "firstname": 
      search = e1; 
      break; 
     case "middlename": 
      search = e2; 
      break; 
     case "lastname": 
      search = e3; 
      break; 
     case "emailaddress": 
      search = e4; 
      break; 
     case "phonenumber": 
      search = e5; 
      break; 
     default: 
      System.out.println("Error"); 
     } 

     System.out.println("search = " + search); 

     try { 
      Class.forName("org.hsqldb.jdbc.JDBCDriver"); 
      Connection conn = DriverManager.getConnection("jdbc:hsqldb:file:///c:/hsqldb/mydb", "SA", ""); 

      Statement stmt = conn.createStatement(); 

      ResultSet rs = stmt.executeQuery(
        "SELECT firstname, middlename, lastname, emailaddress, phonenumber FROM MY_TABLE WHERE '" 
          + columnName + "' = '" + search + "'; "); 

      rs.next(); 
      // while (rs.next()) { 
      text1 = rs.getString("firstname"); 
      text2 = rs.getString("middlename"); 
      text3 = rs.getString("lastname"); 
      text4 = rs.getString("emailaddress"); 
      text5 = rs.getString("phonenumber"); 
      // } 

      // while (rs.next()) { 
      // System.out.println(rs.getRow() + ". " + rs.getString("TITLE") 
      // + "\t" + rs.getString("AUTHOR")); 
      // } 
     } 

     catch (Exception excepton) { 
      excepton.printStackTrace(); 
     } 
     JFrame frame3 = new JFrame("Search result"); 
     frame3.setSize(350, 350); 
     frame3.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     frame3.setLocation(500, 250); 
     JPanel panel2 = new JPanel(); 
     panel2.setLayout(new GridLayout(1, 1)); 
     frame3.add(panel2); 

     JTextArea textArea = new JTextArea(); 
     panel2.add(textArea); 
     textArea.setVisible(true); 

     totalText = " '" + text1 + "' \n '" + text2 + "' \n '" + text3 + "' \n" + " '" + text4 + "' \n '" 
       + text5 + "' "; 
     System.out.println("totalText = " + totalText); 
     textArea.setText(totalText); 

     frame3.setVisible(true); 
    } 
} 

Answer 1

有，据我可以看到它，在你的代码两个错误。

首先，您没有正确构建SQL查询。在将它发送到数据库之前，尝试将其打印出来。你会发现你得到如下内容：

SELECT firstname, middlename, lastname, emailaddress, phonenumber FROM MY_TABLE WHERE 'middlename' = 'Fred'; 

发现错误？ （向右滚动）

您正在从MY_TABLE中选择所有行，其中字符串middleName和（本例中为Fred）是相等的。当然，这些字符串并不相同，所以你没有匹配的行。

你可能想运行下面的查询：

SELECT firstname, middlename, lastname, emailaddress, phonenumber FROM MY_TABLE WHERE middlename = 'Fred'; 

注意，不再有任何引号middlename，所以middlename现在被视为列名，而不是作为一个字符串。如果这是您想要的，请删除columnName变量两侧的SQL字符串中的单引号。

第二个问题是在这里：

 rs.next(); 

你不会费心去检查是否你得到任何结果回来。通过从这个方法返回false，HSQL告诉你没有数据。但是，您选择不听这个，不管怎样都会继续读取数据。

你想，而不是写的是类似如下：

 if (rs.next()) { 
      // read the data out of the result set. 
     } else { 
      // handle the case that no matching data was found. 
     }