get the user_id while inserting a new record to a table

[eluser]max123[/eluser]
I have a table called 'user'. Primary key is 'user_id' and it is an auto increment value. When I'm inserting a new user to the table, I want to get the user_id of that user. What is the sql query to do that

Thanx

[eluser]n0xie[/eluser]

Code:

$this->db->insert_id()