So, now that I have a full day of records, I can now start to get some statistics from my unique visitor tracking test. To get the number of unique visitors coming on the website yesterday, I just run:

SELECT COUNT(*) FROM
   (SELECT DISTINCT "user" FROM indefero_idfa_tracker_logs
    LEFT JOIN indefero_idfa_tracker_users
    ON indefero_idfa_tracker_users.id="user"
    WHERE bot IS FALSE
       AND DATE(indefero_idfa_tracker_logs.creation_dtime) = CURRENT_DATE - 1

    GROUP BY "user")
   AS foo;

This gives me 151 unique visitors. Doing a small check of the indefero_idfa_tracker_users table, I found 2 bots, so 149 unique visitors. Now, let's go and ask Google Analytics and I get 120 absolute unique visitors, a 20% difference. 

Note that the tracking is running on indefero.net, which is a website targeted towards geeks, I think that for this demographic group a 20% difference is not that big, this means that only 20% are blocking the GA tracker code. Anyway, I am really happy with the results and this means that the tracking is working well. My backend is PostgreSQL, with MySQL you may need to adapt your query for the date operation.

Bonus: Changing bot IS FALSE by bot IS TRUE gives me 60 bots and crawlers.