插入新行時出現SQL語法錯誤

Question

以下是我的代碼，用於當用戶單擊應用餘額。這適用於第一部分，用戶的平衡更新很好，但是當我嘗試執行第二條語句時，會出現SQL語法錯誤。什麼可能導致這個問題？

public void mouseClicked(MouseEvent e) { 
      if (cal == true) { 
       try { 
       int balchange = updatebal; 
       String username = (String) userPicker.getSelectedItem(); 
       Connection conn = DriverManager.getConnection(Host, Name, Pass); 
       PreparedStatement pst = conn.prepareStatement("UPDATE table_1 SET user_bal='"+balchange+"' WHERE user_name='"+username+"'"); 
       pst.execute(); 


       String sign = "£"; 
       String PayName = textField_1.getText(); 
       PreparedStatement pst2 = conn.prepareStatement("INSERT INTO payment_info (payment_name, payment_amount, payment_date, username)"+" VALUES ('"+PayName+"', '"+sign+balchange+"', '"+Date+"', '"+username+"'"); 
       pst2.execute(); 
       cal = false; 
       } 
       catch (Exception e3) { 
       e3.printStackTrace(); 
       } 
      } 
      else { 
       JOptionPane.showMessageDialog(null, "Please use the Calculator First!"); 
      } 
     } 

下面是我運行這個時得到的堆棧跟蹤。

com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '' at line 1 
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) 
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) 
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) 
at java.lang.reflect.Constructor.newInstance(Constructor.java:422) 
at com.mysql.jdbc.Util.handleNewInstance(Util.java:404) 
at com.mysql.jdbc.Util.getInstance(Util.java:387) 
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:939) 
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3878) 
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3814) 
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2478) 
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2625) 
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2551) 
at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1861) 
at com.mysql.jdbc.PreparedStatement.execute(PreparedStatement.java:1192) 
at AdminPanelMain$7.mouseClicked(AdminPanelMain.java:444) 
at java.awt.Component.processMouseEvent(Component.java:6538) 
at javax.swing.JComponent.processMouseEvent(JComponent.java:3324) 
at java.awt.Component.processEvent(Component.java:6300) 
at java.awt.Container.processEvent(Container.java:2236) 
at java.awt.Component.dispatchEventImpl(Component.java:4891) 
at java.awt.Container.dispatchEventImpl(Container.java:2294) 
at java.awt.Component.dispatchEvent(Component.java:4713) 
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4888) 
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4534) 
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4466) 
at java.awt.Container.dispatchEventImpl(Container.java:2280) 
at java.awt.Window.dispatchEventImpl(Window.java:2750) 
at java.awt.Component.dispatchEvent(Component.java:4713) 
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758) 
at java.awt.EventQueue.access$500(EventQueue.java:97) 
at java.awt.EventQueue$3.run(EventQueue.java:709) 
at java.awt.EventQueue$3.run(EventQueue.java:703) 
at java.security.AccessController.doPrivileged(Native Method) 
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76) 
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86) 
at java.awt.EventQueue$4.run(EventQueue.java:731) 
at java.awt.EventQueue$4.run(EventQueue.java:729) 
at java.security.AccessController.doPrivileged(Native Method) 
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76) 
at java.awt.EventQueue.dispatchEvent(EventQueue.java:728) 
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201) 
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116) 
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105) 
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101) 
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93) 
at java.awt.EventDispatchThread.run(EventDispatchThread.java:82) 

Answer 1

您的第二個查詢缺少Values子句中的右括號。

而不是直接在查詢中附加參數使用參數化查詢。

public void mouseClicked(MouseEvent e) { 
    if (cal == true) { 
     try { 
     int balchange = updatebal; 
     String username = (String) userPicker.getSelectedItem(); 
     Connection conn = DriverManager.getConnection(Host, Name, Pass); 
     PreparedStatement pst = conn.prepareStatement("UPDATE table_1 SET user_bal=? WHERE user_name=?"); 

     pst.setInt(1, balchange); 
     pst.setString(2, username); 

     pst.execute(); 

     String sign = "£"; 
     String PayName = textField_1.getText(); 
     PreparedStatement pst2 = conn.prepareStatement("INSERT INTO payment_info (payment_name, payment_amount, payment_date, username)" 
     + " VALUES (?, ?, ?, ?)"); 

     pst2.setString(1, PayName); 
     pst2.setString(2, sign + balchange); 
     pst2.setString(3, "Date");//if it's date column use ps2.setDate(3, new Date()); 
     pst2.setString(4, username); 

     pst2.execute(); 
     cal = false; 
     } 
     catch (Exception e3) { 
     e3.printStackTrace(); 
     } 
    } 
    else { 
     JOptionPane.showMessageDialog(null, "Please use the Calculator First!"); 
    } 
} 

這看起來會更清潔，而且會更容易編寫。最重要的是它會爲您節省SQL Injection的攻擊。

這裏是甲骨文的文檔參數化查詢https://docs.oracle.com/javase/tutorial/jdbc/basics/prepared.html

Answer 2

在這裏看看：

PreparedStatement pst2 = conn.prepareStatement("INSERT INTO payment_info (payment_name, payment_amount, payment_date, username)"+" VALUES ('"+PayName+"', '"+sign+balchange+"', '"+Date+"', '"+username+"'") 

好像你沒有在SQL語句中右括號應該是VALUES()不VALUES(的。

順便說一句，有幾個ORM系統，如mybatis或hibernate，爲什麼不選一個呢？它們不僅可以幫助您減少工作，還可以輕鬆訪問數據庫。