I have an application and around 20 accounts are created per minute (on average). I need to implement a new feature which requires the ID of the last insert.
I am using PDO.
The question is, lets say 5 users create accounts at exactly the same time. Will it return the ID from the database for that users profile that was just created, or will it return the last insert?
If you get what I mean.
Assuming MySQL (I don´t think all databases have a last-insert ID functionality like MySQL...), every script will return the ID for the item it has just entered, all instances operate independently.
Will it return the ID from the database for that users profile that was just created, or will it return the last insert?
It will return the last insert id of the current connection session. So even if a new record is created in another instance of the same script, the last insert id will be the one you want.
Example (in psuedo-event form):
Create new user // with id of 5
Sleep for 10 seconds - meanwhile another script inserts 3 users
Fetch the last insert id - this will be 5
You should take a look at the PDO::lastInsertID function: http://de.php.net/manual/en/pdo.lastinsertid.php