Check Key Doesn't Exist

I want to check if a key exists in a MySQL DB. I can do this ok but I would need to create a new key if it does exist.

So this is the function that makes the key:

function keygen($a){
    $b = str_shuffle('abcdefghijklmnopqrstuvwxyz1234567890');
    return substr($b,0,$a);
}

PHP:

So I thought about making a while loop to check if the key exists. But I don't know how to form it.

Could someone explain please. Thanks.

 

There are hashing algorithms for this purpose already, like md5() and sha1().

$id = mysql_insert_id();
$hash = md5("my_salt_{$id}");
$sql = "update row set my_key = '{$hash}'";
$st = mysql_query($sql) or die(mysql_error());

Code (markup):

 

run the query select from table where key="yourkey"

then use mysql_num_rows to see how many rows contain that key (should be 1 or 0 for you)