Group records by time
I have limited SQLite background (and no practice instance), but I'd try grabbing the minutes using
strftime( FORMAT, TIMESTRING, MOD, MOD, ...)with the %M modifier (http://souptonuts.sourceforge.net/readme_sqlite_tutorial.html)
Then divide that by 15 and get the FLOOR of your quotient to figure out which quarter-hour you're in (e.g., 0, 1, 2, or 3)
cast(x as int)Getting the floor value of a number in SQLite?
Strung together it might look something like:
Select cast( (strftime( 'YYYY-MM-DD HH:MI:SS', your_time_field, '%M') / 15) as int) from your_table(you might need to cast before you divide by 15 as well, since strftime probably returns a string)
Then group by the quarter-hour.
Sorry I don't have exact syntax for you, but that approach should enable you to get the functional groupings, after which you can massage the output to make it look how you want.