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POJava - How To Check If Username Already Exists In a MySQL Table
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  1. POJava - How To Check If Username Already Exists In a MySQL Table
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    copied!<p>I want to check whether a <code>username</code> already exists in a <code>database</code> table or not.</p> <p><strong>Java Code:</strong></p> <pre><code>if (e.getSource() == jButton2) { U = jTextField1.getText(); if (jTextField1.getText().trim().equals("")) { JOptionPane.showMessageDialog(this, "Please Write Username !"); } else if (jPasswordField1.getText().equals("")) { JOptionPane.showMessageDialog(this, "Please Write Password !"); } else { try { String Driver = "com.mysql.jdbc.Driver"; String URL = "jdbc:mysql://localhost:3306/LoginForm"; Class.forName(Driver); Connection Conn = DriverManager.getConnection(URL, "root", "12345"); Statement S = Conn.createStatement(); ResultSet RS = S.executeQuery( "SELECT * FROM login where username ='" + U + "' and Password ='" + jPasswordField1.getText() + "'"); while (RS.next()) { String Username = RS.getString("Username"); String Password = RS.getString("Password"); String Admin = RS.getString("Admin"); if (Username.equals(U) &amp; Password.equals(jPasswordField1.getText()) &amp; Admin.equals("0")) { JOptionPane.showMessageDialog(this, "Logged In Successfully !"); this.dispose(); NormalUsers NU = new NormalUsers(); break; } else if (Username.equals(U) &amp; Password.equals(jPasswordField1.getText()) &amp; Admin.equals("1")) { JOptionPane.showMessageDialog(this, "Logged In Successfully , Opening Administration Panel !"); this.dispose(); AdminPanel AP = new AdminPanel(); break; } else { JOptionPane.showMessageDialog(this, "Invalid Username Or Password!"); } } } catch (SQLException | ClassNotFoundException ex) { } } } </code></pre> <p><strong>The problem is that:</strong></p> <ul> <li>If there are no rows in the <code>database</code>, then there is no an error message: <code>Invalid Username or Password</code>. </li> <li>When I execute the <code>SQL</code> query manually: <code>SELECT * From Login</code> I see the row exists there, but since I filter on <code>password</code>, it doesn't get into the <code>while loop</code>.</li> </ul> <p><strong>How should I use java to check if a username exists in a MySQL table?</strong></p>
 

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