How to correctly calculate statistics in MySQL?

Question

MySQL

Good afternoon.
There is a task - to calculate the statistics of transitions on the referral link and the number of registrations by day.
Now it works like this: pastebin.com/X2HKN3cq
Is it possible to optimize somehow or is this the best option for solving such a problem? It used to be simple - selecting rows from the referral table and gluing (JOIN) with the registration table. With this approach, there are several bugs: On days when there were no clicks on the link, statistics are not displayed, if there are more than 1 registrations, then the number of uniques (clicks on the link) is multiplied by the number of regs (the COUNT (DISTINCT id) methods were solved, but in my opinion - it's a crutch!).
How to implement the correct calculation of statistics by day in MySQL?

Answer 1

From date and partner_id, make a composite key like 13-2015-07-04 for example. Make it unique.
When writing, insert 1 into the value or update +1.
When displaying a chart, initially fill with zeros all dates that are empty (at least create an array by period filled with zeros and pour an array from the database into it).