PHP if random code exists in database regenerate random code

Question

I'm attempting to create a PHP script that will create a random code and check it against a database to see if it exists. I'd like it to check that if it exists then generate another createRandomCode() and check it.

Unsure how to proceed with looping until the number of rows are 0.

function createRandomCode($length='6'){ 
    $chars = "abcdefghijkmnopqrstuvwxyz023456789"; 
    srand((double)microtime()*1000000); 
    $i = 0; 
    $code= ''; 
    while ($i++ < $length){ 
        $code = $code. substr($chars, rand() % 33, 1);  
    } 
    return $code; 
}

$shorturl = createRandomCode();

$q = $db - > query("SELECT * FROM maps WHERE url='".$shorturl.
    "'");
if (mysqli_num_rows($q) > 0) {

    $arr = json_encode($arr);
    echo $arr;
}

Please also read up about race conditions.

TimWolla
– TimWolla

2015-05-02 22:30:21 +00:00
Commented May 2, 2015 at 22:30 — TimWolla
– TimWolla, Commented May 2, 2015 at 22:30

AlliterativeAlice · Accepted Answer · 2015-05-02 22:28:41Z

6

Sounds like a good candidate for a do...while loop:

do {
    $shorturl = createRandomCode();
    $q = $db->query("SELECT * FROM maps WHERE url='".$shorturl."'");
} while(mysqli_num_rows($q) > 0);

answered May 2, 2015 at 22:28

AlliterativeAlice

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3 Comments

ngplayground Over a year ago

How would I proceed when mysqli_num_rows === 0

AlliterativeAlice Over a year ago

@Donald After the loop, $shorturl will contain a unique random code. I assume you'd want to insert it into the database at that point.

Tom Over a year ago

I went searching around for the best way to do this and this one is the best. Very elegant and simple.

7uc1f3r · Accepted Answer · 2021-01-11 13:38:37Z

1

function regenerateCode(){

    global $connection;

    do{

        $serial2 = rand(0,7);

        $check_code = "SELECT * FROM `voters` WHERE `serial` = '$serial2'";

        $run_check_code = mysqli_query($connection,$check_code);

        $count = mysqli_num_rows($run_check_code);

    } while( $count > 0 );

    return $serial2;
}

edited Jan 11, 2021 at 13:38

7uc1f3r

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answered Jan 11, 2021 at 13:15

SABS-TECH

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1 Comment

7uc1f3r Over a year ago

While this code may answer the question, it would be better to include some context, explaining how it works and when to use it. Code-only answers are not useful in the long run.

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