Question

I’m having a bit of a problem when it comes to a single mySQL script; specifically, mySQL keeps giving me this error:

MySQL Error: Duplicate entry '39835a3f63f222c9bf51d9dd471b90bc' for key 'PRIMARY'

It’s pretty weird cause the primary key in question is a MD5 generated hash based off of the time() function of php, so there shouldn’t be any issues.

This is the php code that inserts into the table:

INSERT INTO log
    (hailID, timestamp, lat, lng, phone, device, method, serviceType, email, address, languageID, ipaddress)
        VALUES
    (MD5('" . $time . $data['phone'] . "'),
     '$time',
     '".$data['lat']."',
     '".$data['lng']."',
     '".$data['phone']."',
     '".$data['device']."',
     '".$data['method']."',
     '".$data['serviceType']."',
     '".$data['email']."',
     '".$data['address']."',
     '".$data['languageID']."',
     '".$_SERVER["REMOTE_ADDR"]."'

$time in this case, is just a variable holding the value from the time() function. Funnily enough, this problem isn’t very frequent, and it appears to be random (at least as far as I can tell). And yes, all the data is sanitized using mysqli_escape_string() before it goes into the $data array. I’ve also checked my table using CHECK TABLE and no errors have appeared either.

Any ideas?

Thanks

Answer 1

If 2 entries are logged within the same second they will have the same hash value. This will happen more frequently than you think on even a fairly low-use system. I would suggest:

1. Do away with the hash. Store the current time as DATETIME or TIMESTAMP using NOW(). You’ll actually have a sortable table.
2. Use a surrogate key in the log file, ie an INT with AUTO_INCREMENT
3. If you need to store an exact, unique time and avoid duplicates look into PHP’s microtime() function.

Think about it, even if you stored the ID as an 8-byte BIGINT it’s still 4x smaller than the VARCHAR(32) that you need to store an MD5 hash.