myquery错误:“where子句中的null |未知列”

pgccezyw  于 2021-06-25  发布在  Mysql
关注(0)|答案(3)|浏览(273)

这是我的高级项目。请记住我还是个初学者。
因此,我想创建一个搜索应用程序,用户将从jcombobox中选择一个“专业”,一旦他们单击“搜索”,该应用程序将从mysql数据库检索数据并在jtable中显示。
因为我不擅长编程,所以我遵循了一些教程,我被这个错误困住了:
“where子句”中的未知列“architecture”
“架构”是jcombobox中的选项之一,但我认为sql将它作为一列来读取,尽管它是一行!
我的问题是:

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;
   }
}

&

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);
            }

            }

    });
h9vpoimq

h9vpoimq1#

更好的解决方法是使用 PreparedStatement --如果你的特长是 Being "cool" ,即使它包含引号字符。
准备好的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();
nbnkbykc

nbnkbykc2#

试着用引号括住输入:

rows = st.executeQuery("SELECT * FROM mydb.applications WHERE speciality LIKE '" + speciality + "'");
c6ubokkw

c6ubokkw3#

这里的问题在于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+"'");

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