Generating Unique String in PHP for Mysql Database

Question

How can I generate a unique Key and insert it into my mysql database?
This is what I currently use:

echo uniqid(time(), true);

Can you tell me wether it is a unique key or not?

Answer 1

You can use AUTOINCREMENT on your id field in the database.
It will never get duplicate since it increments the highest existing id present.

Answer 2

you can use following to get unique id with 32 chars

md5(uniqid(time(), true))

or you can use sha1 like with 40 chars

sha1(uniqid(time(), true))