尝试使用数据库构建简单的应用程序

Question

我正在尝试构建一个仅用于保存记录的应用程序，现在将其删除，我是Java和数据库的新手，当我保存它时可以正常工作，但是当我尝试删除它时出现错误：

Comparisons between 'LONG VARCHAR (UCS_BASIC)' and 
    'LONG VARCHAR (UCS_BASIC)' are not supported.

---

private void SaveBtnActionPerformed(java.awt.event.ActionEvent evt) {
    try{
        conn = DriverManager.getConnection("jdbc:derby://localhost:1527/Test", "app", "testcode");
        st = (Statement) conn.createStatement();
        String sql = "INSERT INTO APP.UNTI(ID,NAME) VALUES(?,?)";
        PreparedStatement ps = conn.prepareStatement(sql);
        ps.setString(1, J1.getText().trim());
        ps.setString(2, J2.getText().trim());
        if(ps.executeUpdate()>0){
            JOptionPane.showMessageDialog(null, "insert succusful");
        }
    }catch(SQLException xmp){
       System.out.println("error");
    }
}                                       

private void RemoveBtnActionPerformed(java.awt.event.ActionEvent evt) {                                          
    // TODO add your handling code here:
      try{
        conn = DriverManager.getConnection("jdbc:derby://localhost:1527/Test", "app", "testcode");
        st = (Statement) conn.createStatement();            
        PreparedStatement ps = conn.prepareStatement("DELETE FROM UNTI WHERE NAME = ? ");
        System.out.println("ok");
        ps.setString(1,J2.getText().trim());           
        if(ps.executeUpdate() > 0){
            JOptionPane.showMessageDialog(null, "insert succusful");
        }
    }catch(SQLException xmp){
       System.out.println(xmp.getMessage()  );
    }catch(NullPointerException xmp){
        System.out.println(xmp.getMessage()  );
    }

}     

Answer 1

您无法比较长varchar，就像无法索引它们一样。

Comparison table documentation

图片取自文档（提供链接），请注意，不能将long varchar与long varchar进行比较。

Derby issue about this already registered

建议：

根据您的数据，我建议使用varchar或CLOB而不是long varchar。