如何根据条件从MySQL数据库中读取数值？

huangapple
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英文:

How to read value from mysql database based on condition?

问题

我正在进行一个Java项目，允许用户根据他们在帐户创建时选择的角色登录为管理员或用户。我已经成功编写了代码，在我的应用程序的登录页面上检查他们的用户名和密码是否正确，方法是检查这些值是否存在于数据库中。然而，我想让用户以管理员或用户的身份登录，但我不知道如何实现。我考虑如果我可以从数据库中读取他们在帐户创建时选择的角色（用户或管理员），然后可以基于这个值编写一个条件语句。例如，如果(usertype == 'admin'){ // 转到管理员页面} 但是usertype是数据库中的一列，我不知道如何读取它。下面是我的代码，这是一个在按下登录按钮时激活的函数。如果你知道解决方案，请告诉我，谢谢。

  1. private void LoginButtonActionPerformed(java.awt.event.ActionEvent evt) {
  2.     Connection con;
  3.     PreparedStatement pst;
  4.     ResultSet rs;                                            
  5.     try {
  6.         String query = "SELECT * FROM `accounts` WHERE username=? and password=?"; // and usertype=?
  7.         con = DriverManager.getConnection("jdbc:mysql://localhost/restock", "root", "password");
  8.         pst = con.prepareStatement(query);
  9.         pst.setString(1, txtUsername.getText());
  10.         pst.setString(2, txtPassword.getText());
  11.         rs = pst.executeQuery();
  12.         if (rs.next()) {
  13.             JOptionPane.showMessageDialog(this, "Login is successful as admin");
  14.             mainpage admin = new mainpage();
  15.             admin.setVisible(true);
  16.             dispose();
  17.         } else {
  18.             JOptionPane.showMessageDialog(this, "Incorrect username or password");
  19.             /*usermainpage user = new usermainpage();
  20.             user.setVisible(true);
  21.             dispose();*/
  22.         }
  23.     } catch (Exception ex) {
  24.         JOptionPane.showMessageDialog(this, ex.getMessage());
  25.     }
  26. }

这是我的数据库中的列的图片：
如何根据条件从MySQL数据库中读取数值？

  2. <details>
  3. <summary>英文:</summary>
  5. I am doing a Java project to allow users to either log in as an admin or user based on what they selected from their account creation. I managed to do a code to check if their username and password were correct in my login page of the application by checking if those values are present in the database, however, I want the user to login as either an admin or user but I don&#39;t know how to do that. Im thinking if I can read what they selected as (either user or admin) from their account creation in the database (refer below for picture of database columns), then I am able to do an if statement based on that. For example if(usertype == &#39;admin&#39;){ // then go to admin page} But usertype is a column in the database which I don&#39;t know how to read.I have my code below as well which is function that activates whenever the login button is pressed.If you know of a solution, let me know thank you.    
  7.     private void LoginButtonActionPerformed(java.awt.event.ActionEvent evt) {
  8.         Connection con;
  9.         PreparedStatement pst;
  10.         ResultSet rs;                                            
  11.             try{
  12.                 String query = &quot;SELECT * FROM `accounts` WHERE username=? and password=?&quot;; // and usertype=?
  13.                 con = DriverManager.getConnection(&quot;jdbc:mysql://localhost/restock&quot;, &quot;root&quot;, &quot;password&quot;);
  14.                 pst = con.prepareStatement(query);
  15.                 pst.setString(1, txtUsername.getText());
  16.                 pst.setString(2, txtPassword.getText());
  17.                 rs = pst.executeQuery();
  18.                 if(rs.next()){
  19.                     
  20.                     JOptionPane.showMessageDialog(this, &quot;Login is successful as admin&quot;);
  21.                     mainpage admin = new mainpage();
  22.                     admin.setVisible(true);
  23.                     dispose();
  24.                 }
  25.                 else{
  26.                     JOptionPane.showMessageDialog(this, &quot;Incorrect username or password&quot;);
  27.                     /*usermainpage user = new usermainpage();
  28.                     user.setVisible(true);
  29.                     dispose();*/
  30.                 }
  31.                 
  32.             } catch(Exception ex){
  33.                 JOptionPane.showMessageDialog(this, ex.getMessage());
  34.             }
  35.             
  36.             
  37.             
  38.         }  
  41. This is a picture of the columns that are in my database
  42. [![enter image description here][1]][1]
  44.                 
  47.   [1]: https://i.stack.imgur.com/RqV5m.png
  49. </details>
  52. # 答案1
  53. **得分**: 1
  55. 由于你正在执行SELECT *，你应该能够在你的Java代码中通过以下方式访问usertype：
  57. ```java
  58. if(rs.next()){
  59.     String userType = rs.getString("usertype");
  60.     if(userType.equals("admin")){
  61.         // 这里是你的管理员代码
  62.     }else{
  63.         // 这里是你的用户代码
  64.     }
  65. }
英文:

Since you're doing a SELECT *, you should be able to access the usertype in your java code with something like

  1. if(rs.next()){
  2.     String userType = rs.getString(&quot;usertype&quot;);
  3.     if(userType.equals(&quot;admin&quot;)){
  4.         // your admin code here
  5.     }else{
  6.         // your user code here
  7.     }
  8. }

huangapple
  • 本文由 发表于 2020年8月6日 23:49:23
  • 转载请务必保留本文链接：https://go.coder-hub.com/63287310.html
  • java
  • mysql
  • netbeans
  • sql
  • swing
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