I'm not sure why this is being upvoted. It's very light on technical content (how can you mention sqlite and not say that its type system is advisory only is beyond me), and provides no added value compared to what you can get out of a quick google search if you wanted to compare these three widely used RDBMS.

I'll note that I usually disagree with these "why is this on HN" posts, but technical posts should have a higher bar than this.