Unique ID with time()

Question

If I use:

$t = time();
echo $t;

This will output something like: 1319390934

I have two questions:

This value can be used as unique id ?
how to generate from it a date?

I can't use uniqid(), because I need a value that can be used to order (recent).

Unique in what context? How are you using the ID? (`microtime()` is also typically used for unique ID's). — Jared Farrish, Oct 23 '11 at 17:38
in this case a number that can't be repeated. like an unique index in sql. — user947462, Oct 23 '11 at 17:40
No, I mean, do you want to prevent collisions between rows *per user*, or rows *for all users*? Or some other condition? What do you need a unique ID *for*? — Jared Farrish, Oct 23 '11 at 17:44
By the way uniqid is also ordered. It's just an encoded microtime, basically. — NikiC, Oct 23 '11 at 17:51

Seralize · Accepted Answer · 2011-10-23T18:38:31.873

15

Using time() as mentioned will give you a sortable way to create unique IDs. Concatenating strings will also further randomize your desired result and still keep it sortable:

$uniqueId= time().'-'.mt_rand();

edited Oct 23 '11 at 18:38

answered Oct 23 '11 at 17:43

Seralize

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Yes make sure you at mt_rand, other wise two or more users could have the same unique id if they come at exactly the same time. – Mike Oct 23 '11 at 18:44

score 4 · Answer 2 · edited May 23 '17 at 12:25

Obviously this cannot be used as a "unique" id because, well, it's not unique during the duration of the same second.
Look into date.

If you want something that is advertised as a unique id and both can be sorted, you can use something like this that involves uniqid:

$u = time().'-'.uniqid(true);

I 'm perhaps over-simplifying here, taking for granted that all values time is going to produce will have the same number of digits (so that a string sort would produce the same results as a natural sort). If you don't want to make this assumption, then you could consider

$u = sprintf("%010s-%s", time(), uniqid(true));

Since it's for a database, an `auto_increment` column paired with a `NOW()` column could also work, depending on the use. — Jared Farrish, Oct 23 '11 at 17:46

score 1 · Answer 3 · answered Oct 23 '11 at 17:46

If you are using this code in an environment where you have a user account with a unique ID, you can append time() to their account ID to generate a unique ID.

You can turn time() back into a date string using:

$time = time();
echo 'The datestamp for (' . $time . ') is ' . date("Y-m-d", $time);

Of course the date format can be altered using any of PHP's date() format.

score 0 · Answer 4 · answered Oct 25 '21 at 16:27

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I would probably do this:

$id = microtime();

answered Oct 25 '21 at 16:27

Jens Törnell

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Unique ID with time()

4 Answers4