php - MySQLi creating random string, but checking it doesn't already exist -

below code have written create random string. works well. checks make sure generated string doesn't exist, , if does, makes one. haven't yet worked out way make code generated if 1 exists checked see if 1 exists. best doing elseif statement?

php

<?php require_once('dbconfig.php'); $randomstring = ''; $characters = '0123456789abcdefghijklmnopqrstuvwxyz';  ($i = 0; $i < 12; $i++) {     $randomstring .= $characters[rand(0, strlen($characters) - 1)]; } //$generatedid = "spi-e7hn2sbiif5w"; $generatedid = 'spi-'.$randomstring;  //prepare select query $statement = $db->prepare("select client_unique_id clients client_unique_id = ? limit 1");  //determine variable , bind variable parameter select query ? $id = $generatedid; $statement->bind_param('s', $id);  //execute , store result num_rows returns value , not 0 $statement->execute(); $statement->store_result();  //bind result variable easy management afterwards $statement->bind_result($clientid);  // generate random id user if generated 1 exists if($statement->num_rows > 0){     $randomstring = '';     $characters = '0123456789abcdefghijklmnopqrstuvwxyz';      ($i = 0; $i < 0; $i++) {         $randomstring .= $characters[rand(0, strlen($characters) - 1)];     }     $generatedid = 'spi-'.$randomstring;     echo $generatedid; } else {     // if there's no issue what's been created, echo out :)     echo $generatedid; }   ?> 

any appreciated :)

try this.

// initialize variable hold last generated id,  $generatedid = ''; // , hold returned client_unique_id,  $clientid = '';  setup prepared statement bind parameter,  $statement->bind_param('s', $id) {    generate new id. (code generating random id goes here).    $generatedid = '...';    // bind generated id prepared statement.     $id = $generatedid    // execute prepared statement,     $statement->execute()    // fetch results $clientid    $statement->bind_result($res);    while($statement->fetch()) {        $clientid = $res;    } } while ($clientid != '');  $statement->close(); // echo last generated id echo $generatedid; 

cheers,

william