How can I make sure that PDO's lastInsertId() is not that of another simultaneous insert?

Question

I am doing a signup form with an INSERT SQL query using PDO. After this INSERT, I want to extract the userid (auto incrementing, primary key) that was just created, and INSERT it into another table (a "confirmation code" table)

But how can I make sure that this userid is not that of a second user who registered 1/1000th of a second later that the first user?

Should I find some way of locking the table? Should I use transactions?

Answer 1

lastInsertId() returns the identifier of the last row inserted on that connection, so concurrent users (with different connections to the database) will not interfere.

Answer 2

You can avoid this by doing a select by the email or some unique field. That will guarantee you get the correct user id.

For example:

select id from user_table where email = '[email protected]' limit 1;