php - How do I tell the user their email is already registered?

Solution:

As per the comment - if you do a simple before trying to do the{-code-2} you can fork the program logic and let the user know.

<?php

    if( $_SERVER['REQUEST_METHOD']=='POST' && isset( 
        $_POST['fullname'], 
        $_POST['email'], 
        $_POST['mobilenumber'] 
    )){
        
        $fullname = $_POST['fullname'];
        $email = $_POST['email'];
        $mobilenumber = $_POST['mobilenumber'];
        
        
        
        $dbport =   3306;
        $dbhost =   'localhost';
        $dbuser =   'dbo-user-xxx';
        $dbpwd  =   'dbo-pwd-xxx';
        $dbname =   'db-xxx';
        
        
        
        error_reporting( E_ALL );
        mysqli_report( MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT );
        $conn = new mysqli( $dbhost, $dbuser, $dbpwd, $dbname );
        
        try{
        
            #check email before {-code-2}
            $sql=' `email` from `signup` where `email`=?';
            $stmt=$conn->prepare( $sql );
            $stmt->bind_param('s',$email);
            $stmt->execute();
            $stmt->store_result();
            
            if( $stmt->num_rows==0 ){
                /* email does not exist - perform {-code-2} */
                $sql='{-code-2} into `signup` ( `fullname`, `email`, `mobilenumber` ) values ( ?, ?, ? )';
                $stmt=$conn->prepare( $sql );
                $stmt->bind_param('sss', $fullname, $email, $mobilenumber );
                $stmt->execute();
                $stmt->close();
                $conn->close();
                
                exit( header('Location: thankyou.html') );
                
            }else{
                /* email does exist - tell user */
                $stmt->free_result();
                $stmt->close();
                
                exit( header('Location: ?error=true&email=true' ) );
            }
            
        }catch( mysqli_sql_exception $e ){
            exit( $e->getMessage() );
        }
    }
?>
Copy code

Alternatively you can{-code-4} as before but use the return error code to fork the logic

<?php
    /*
    
        mysql> describe signup;
        +     

Solution:

  // first check the database to make sure 
  // a email does not already exist with the same  email
  $fullname = $_POST['fullname'];
  $email = $_POST['email'];
  $mobilenumber = $_POST['mobilenumber'];

  $user_check_query = "SELECT * FROM signup WHERE email='$email'LIMIT 1";
  $result = mysqli_query($cons, $user_check_query);
  $emailcheck= mysqli_fetch_assoc($result);
  
  if ($emailcheck) { // if email exists
    if ($emailcheck['email'] === $email) {
      array_push($errors, "email already exists");
    header('location: index.php');
    }

  }

  // Finally, register user if there are no errors in the form
  if (count($errors) == 0) {
     $sql = "insert into 
     signup(fullname,email,mobilenumber)values($fullname,$email,$mobilenumber)";
     $runsql = mysqli_query($cons, $sql);

    if($runsql) {
        header("Location:thankyou.html");
    } else {
        echo"Some thing is wrong";
    }
  }
}
Copy code