Question

这是我的高级项目。请记住，我还是初学者。

所以我想创建一个搜索应用，用户将选择一个专业＆＃39;从JComboBox开始，一旦他们点击“搜索”，该应用程序将从MySQL数据库中检索数据并将其显示在JTable中。

由于我不是编程方面的专家，所以我遵循了一些教程，并且我坚持这个错误：

未知专栏＆＃39;架构＆＃39;在＆＃39; where子句＆＃39;

＆＃39;建筑＆＃39;是JComboBox中的选项之一，但我认为SQL将其作为列读取，尽管它是一行！

这是我的查询：

public class MyQuery {

   public Connection getConnection(){
        Connection con = null;
        try {
            con = DriverManager.getConnection("jdbc:mysql://localhost:3306/mydata?autoReconnect=true&useSSL=false", "root", "1110");
        } catch (SQLException ex) {
            Logger.getLogger(Query.class.getName()).log(Level.SEVERE, null, ex);
        }
        return con;
    }

    public ArrayList<Applications> getData(String speciality){

   ArrayList<Applications> list = new ArrayList<Applications>();
   Connection con = getConnection();
   Statement st;
   ResultSet rows;

   try {
   st = con.createStatement();

   rows = st.executeQuery("SELECT * FROM mydb.applications WHERE speciality LIKE " + speciality);

   Applications applications;
   while(rows.next()){
   applications = new Applications(
   rows.getInt("id"),
   rows.getString("name"),
   rows.getString("nationality"),
   rows.getString("speciality"),
   rows.getString("experience")
   );

   list.add(applications);
   }

   } catch (SQLException ex) {
   Logger.getLogger(MyQuery.class.getName()).log(Level.SEVERE, null, ex);
   }
   return list;
   }
}

＆安培;

        JButton btnSearch = new JButton("Search...\n");
    btnSearch.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {

            MyQuery mq = new MyQuery();
            ArrayList<Applications> list = mq.getData((String)comboBox_searchSp.getSelectedItem());
            DefaultTableModel model = new DefaultTableModel();
            model.setColumnIdentifiers(new Object[]{"ID","Name","Nationality","Speciality","Experience"});
            Object[] row = new Object[5];
            for(int i = 0; i < list.size(); i++){
                row[0] = list.get(i).getName();
                row[1] = list.get(i).getNationality();
                row[2] = list.get(i).getSpeciality();
                row[3] = list.get(i).getExperience();
                model.addRow(row);
            }
            table.setModel(model);

        }

            public void BindCombo(){

            MyQuery mq = new MyQuery();
            Connection con =  mq.getConnection();
            Statement st;
            ResultSet rows;

            try {
                st = con.createStatement();
                rows = st.executeQuery("SELECT `id`, `name` FROM mydb.applications");
                while(rows.next()){
                    comboBox_searchSp.addItem(rows.getInt(1));
                }
            } catch (SQLException ex) {
                Logger.getLogger(AdminPage.class.getName()).log(Level.SEVERE, null, ex);
            }

            }

    });

Answer 1

更好的解决方案是使用PreparedStatement - 如果您的某个专业是Being "cool"，即使它包含引号字符，您也不会遇到麻烦。

Prepared语句还可以保护您免受SQL注入攻击。

PreparedStatement ps = connection.prepareStatement(
    "SELECT * FROM mydb.applications WHERE speciality LIKE ?");
ps.setString(1, specialty);
ResultSet rs = ps.executeQuery();

Answer 2

尝试在输入周围添加引号：

rows = st.executeQuery("SELECT * FROM mydb.applications WHERE speciality LIKE '" + speciality + "'");

Answer 3

这里的问题在于您的SQL查询语法：

rows = st.executeQuery("SELECT * FROM mydb.applications WHERE speciality LIKE " + speciality);

应该是：

rows = st.executeQuery("SELECT * FROM mydb.applications WHERE speciality LIKE '" + speciality+"'");

MyQuery错误：＆＃34; null | ＆＃39; where子句＆＃39;＆＃34;中的未知列

3 个答案: