So, couple of days ago, some guy, from Periscope company wrote a blogpost about getting number of distinct elements, per group, faster using subqueries.

This was then submitted to Hacker News and r/Programming on Reddit.

Then, the original authors submitted second blogpost comparing speed between four different DB engines. Which, in turn, was also commented on Reddit.

I found the numbers presented by Periscope (as their improvement) as not that great.

Unfortunately – their blog doesn't allow for comments, so I decided to test it, and write on my own blog, what I can find about it.

Continue reading Getting count of distinct elements, per group, in PostgreSQL.