How to reset UID number back to default order? I have a Drupal 7 website with only UID1 user which is root admin. I deleted previous users. Now if I create a new user, it gets UID of e.g. 74.

It should be UID 2 and so on.

Anyway, I had same problem with resetting nodes back to 1. And I did it by following this answer, but it worked only if you have no nodes. Now, I have at least one user and I don't know if that query would work for 'users'.
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.