I Use PHP and Query My Generates Code Some Time Continues To Run in Processlist Phpmyadmin

i have function to generate random uniq code and check this uniq code in table. In this function i use do while if uniq code available in table. But i have some problem, some time i get mysql query to check uniq code in table always running on my SHOW PROCESSLIST in phpmyadmin. would you help me? Trims

function random($db){
    
    $tgl=date('j');
    $bulan=date('m');
    $front=$tgl;
    
    $rowcount=0;
    $loop_on=0;
    do{
        $randomString = '';
        $characters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890';
        $characters2 = '1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ';
        $characters3 = 'ABCDEFGHIJKLMNOPQRSTUVWXY1234567890';
        $charactersLength = strlen($characters);
        $charactersLength2 = strlen($characters2);
        $charactersLength3 = strlen($characters3);
        
        for ($i = 0; $i < 2; $i++) {
            $randomString .= $characters[rand(0, $charactersLength - 1)];
        }
        for ($i = 0; $i < 2; $i++) {
            $randomString .= $characters2[rand(0, $charactersLength2 - 1)];
        }
        
        $generate = $front.$randomString;
        $sql="SELECT _code FROM antre_ WHERE _code = '$generate'";
        if ($result=$db->get_results($sql))
        {
            $rowcount=count($result);
        }
        $loop_on++;
    }
    while($rowcount>0 || $loop_on==10);
    
    return $generate;
}