选择查询，将出现在 Netbeans 和 mysql 中的组合框中

Question

我的代码有问题：
String charitysql = "SELECT wardName, charityRoomID FROM tbl_charityward,tbl_charityroom2 <br>WHERE tbl_charityward.charityWardID = tbl_charityroom2.charityWardID";<br>

 try { 

        pst = conn.prepareStatement(charitysql);
        rs = pst.executeQuery();

            while (rs.next()) {
                String wardname = rs.getString("wardName");
                cb_ward2.addItem(wardname);
                String roomid = rs.getString("charityRoomID");
                cb_room2.addItem(roomid);                    

            }

        }
        catch(Exception e) {
            JOptionPane.showMessageDialog(null, e);
        }

这是我的表格结构：
tbl_charityward
charityWardID int NOT NULL AUTO_INCREMENT,
wardName varchar(20),
status varchar(20),
PRIMARY KEY (charityWardID)

tbl_charityRoom2
charityRoomID INT NOT NULL AUTO_INCREMENT,
status varchar(20),
charityWardID int,
PRIMARY KEY (charityRoomID, charityWardID),
FOREIGN KEY (charityWardID) REFERENCES tbl_charityward (charityWardID)

这是我的带有值的表格：
tbl_charityward
+-------------+----------+--------+
|charityWardID| wardName | status |
+-------------+----------+--------+
|......1......| Surgical |..Open..|
|......2......| .Obygine |..Open..|
|......3......| Pediatric|..Open..|
+-------------+----------+--------+


tbl_charityroom2
+-------------+--------+-------------+
|charityRoomID|状态 |charityWardID|
+-------------+--------+-------------+
|......1......|..打开..|......1......|
|......2......|..打开..|......1......|
|......3......|..打开..|......2......|
+-------------+--------+-------------+

我有 2 个组合框：
cb_ward2 = which contains wardName<br> cb_room2 = which contains CharityRoomID

如果我从cb_ward2 中选择一个wardName，那么cb_room2 将显示相应的charityRoomID。

示例：
我选择Surgical，charityRoomID = 1, 2 将出现在cb_room2，
当我选择Obygine 时，charityRoomID = 3 只会出现在cb_room2，
但是当我选择Pediatric 时，没有charityRoomID will appear on cb_room2

我正在使用 Netbeans 和 MYSQL

---

编辑：

导入 java.sql.*;

导入 javax.swing.*;

公共类 addBed 扩展 javax.swing.JFrame {

    连接 conn = null;
    结果集 rs = null;
    PreparedStatement pst = null;

    /**
     * 创建新表单 addBed
     */
    公共添加床（）{
        初始化组件（）；
    }

    无效负载组合（）{


            尝试 {


            字符串charitysql =“从tbl_charityward选择病房名称，charityRoomID，tbl_charityroom2 WHERE tbl_charityward.charityWardID =？”；
            pst = conn.prepareStatement(charitysql);
            pst.setInt(1,tbl_charityroom2.charityWardID);
            rs = pst.executeQuery();

                而（rs.next（））{

                    cb_ward2.addItem(rs.getString(1));

                    cb_room2.addItem(rs.getString(2));

                }

            }
            捕获（异常 e）{
                JOptionPane.showMessageDialog(null, e);
            }




    }
    私人无效formWindowOpened（java.awt.event.WindowEvent evt）{
       conn = myconn.ConnectDb();
       加载组合（）；
    }

    私人无效btn_add2ActionPerformed（java.awt.event.ActionEvent evt）{

    }

Answer 1

你使用的方式不是使用 PreparedStatement 的正确方式

这样做

String charitysql = "SELECT wardName, charityRoomID FROM tbl_charityward,tbl_charityroom2 
WHERE tbl_charityward.charityWardID = ?";
pst = conn.prepareStatement(charitysql);
pst.setInt(1,tbl_charityroom2.charityWardID);
rs = pst.executeQuery();

Answer 2

由于您的基本要求是将数据显示为两个ComboBoxes，您可以这样做：

您可以使用loadcombo() 来加载带有数据库值的cb_ward2 组合框。

void loadcombo() {
    try
    {
     Connection conn=null;
 PreparedStatement pst=null;
 ResultSet rs=null;
// Your database connections 

     String charitysql = "SELECT wardName FROM tbl_charityward";
     pst = conn.prepareStatement(charitysql);
     rs = pst.executeQuery();
    while(rs.next()){                            
        cb_ward2.addItem(rs.getString(1));
    }
    con.close();
    }
    catch(Exception e)
    {
        System.out.println("Error"+e);
    }    
}

现在您可以在cb_ward2 上使用ActionListener 作为：

cb_ward2.addActionListener(new ActionListener(){


    public void actionPerformed(ActionEvent ae){
        try
    {
        Connection con=null;
        PreparedStatement pst=null,pst1=null;
        ResultSet rs=null,rs1=null;
    //your database connection
                Object name=cb_ward2.getSelectedItem();
                    pst=con.preparedStatement("select charityWardID from tbl_charityward where wardName=?");
                pst.setObject(1,name);
                    rs= pst.executeQuery();
        if(rs.next())
        {
                      pst1=con.preparedStatement("select charityRoomID from tbl_charityroom2 where charityWardID=?");
                      pst1.setInt(1,rs.getInt(1));
                      rs1=pst1.executeQuery();
                      while(rs1.next()){
                      cb_room2.addItem(rs1.getInt(1));
                      }
            }
                con.close();
    }
    catch(Exception e)
    {
        System.out.println("GG"+e);
    }

    }


    });

Answer 3

尝试使用数组列表！它会给你一个类似推的效果

类似的东西

    ArrayList<String> categories = new ArrayList<>();
    Connection conn = null;
    Statement stmt = null;
    ResultSet rs = null;
    try {
        System.out.println("\ntrying connection");
        conn = DriverManager.getConnection("jdbc:mysql://localhost/products?user=root&password=");
        stmt = conn.createStatement();
        rs = stmt.executeQuery("SELECT DISTINCT categorie FROM product");
        while (rs.next()) {
            categories.add(rs.getString(1));
        }
        for (String item : categories) {
            ComboBoxCategorie.addItem(item);
        }

    } catch (SQLException ex) {
        System.out.println("SQLException: " + ex.getMessage());
        System.out.println("SQLState: " + ex.getSQLState());
        System.out.println("VendorError: " + ex.getErrorCode());
    } finally {
        if (stmt != null) {
            try {
                stmt.close();
            } catch (SQLException sqlEx) {
            } // ignore
            stmt = null;
        }
    }

你可以忽略 catch 和 finally 子句！！只需关闭 stmt