How do you suggest unique usernames to user in PHP?

Question

Let's say the username someone wants is taken, then I want the system to suggest a list of available usernames, say 5 suggestions.

Now, I can generate several usernames based on permutations and combinations of data I already have, like their name, birthday, e.t.c. But how do I make sure those generated usernames are available? I mean, if for each generated username, I have to query the database to check availability, in the worst case scenario this might become something like an infinite loop.

Any ideas?

Answer 1

I suspect the question is a base one so I'll provide a simple example:

<?php

// Untested code and only one of the many possible ideas
$suggestions = array(
    'foobar' => TRUE,
    'foo1974' => TRUE,
    'foo37' => TRUE,
    'drfoo' => TRUE,
    'mrfoo' => TRUE,
);


$params = $placeholders = array();
foreach(array_keys($suggestions) as $position => $username){
    $params['u' . $position] = $username;
    $placeholders[] = ':u' . $position;
}
$sql = 'SELECT username
    FROM user
    WHERE username IN (' . implode(', ', $placeholders) . ')';

$res = $conn->prepare($sql);
$res->execute($params);
while( $row = $res->fetch(PDO::FETCH_ASSOC) ){
    $suggestions[ $row['username'] ] = FALSE;
}


foreach($suggestions as $username => $available){
    if($available){
        // ...
    }
}

Edit:

The only way to provide an infinite list of available names is to use a very simple rule such as adding a consecutive number. In such case, you can try something like this:

SELECT username
FROM user
WHERE username REGEXP '^foo[0-9]+'

... and then:

$username = 'foo';

$suggestions = array();
$count = 0;
$names_left = 5;
while($names_left>0){
    $count++;

    if( !in_array($username . $count, $names_taken) ){
        $suggestions[] = $username . $count;
        $names_left--;
    }
}