什么是PHP中的代码来检查用户是否已经存在？

Question

I'm new in php and mysql. I'm trying to check if the user is already taken or not. If it's taken then it won't added to the database. However, I tried a lot of code to do this trick but none of the code I used worked. I'm not sure what I'm doing wrong. This what I have right now:

<?php

include 'db_settings.php';

db_connect();

//Escape variables for security
$user = mysqli_real_escape_string($con, $_POST['user']);
$pass = mysqli_real_escape_string($con, $_POST['pass']);
$email = mysqli_real_escape_string($con, $_POST['email']);
$sql="INSERT INTO users (user, pass, email)
        VALUES ('$user','$pass', '$email')";


if (!mysqli_query($con,$sql)) {
    die('Error: ' . mysqli_error($con));
}

echo "1 record added</br>";

mysqli_close($con);

echo "<a href='sign-up.html'>sing-up again!</a></br>";
echo "<a href='index.html'> Go Back Home </a>";

?>`

I know this code don't have the checking function for the user if already taken or not because I deleted all the codes about it. So if it's possible if you could guys help me I will appreciate it.

Answer 1

Your code seems to be fine do one thing run the below code on your mysql console or phpMyadmin

ALTER TABLE  `users` ADD UNIQUE (
`user`
);