Every now and then someone asks, on irc or mailing lists, some question which shows deep misunerstanding (or lack of understanding) of timestamps – especially the ones with time zones.
Since I got bitten by this before, let me describe what timestamps are, how to work with them, and what are the most common pitfalls that you can encounter.
Today some guy on IRC asked question, which I didn't fully understand, but which could (probably) be summarized: how to group data into 5 minute intervals, based on some timestamp column.
Well, it seems trivial (as long as you know how to do it), but since he clearly didn't know how to do it (or I misunderstood his problem), here's the explanation:
MySQL has this nifty/annoying feature/bug of special data type “TIMESTAMP". It is like a DATETIME, but it gets automatically updated whenever you modify the row.
I'll try to add the same feature to PostgreSQL.