How to reset UID number back to default order?
I've found the discussion thread about the issue about why users table is not auto-increment and creating a new sequences table for that purpose.


  This is NOT a full sequences API not at all but it's enough for some uses. actions_aid and simpletest_test_id , that's duplicate code not to mention it belongs to the DB layer. This patch solves that. Further work: we can reuse this for users.uid as that should not be serial because of the known problems. The postgresql folks can create a version which uses proper sequences. The mysql folks can support more than the single serial mysql allows -- like a timestamp and a serial. Sorry for the hasty writeup.


In your case, you just update the value in sequences table to 1.

AND

You need to run ALTER TABLE sequences AUTO_INCREMENT = 1 as well.