date_trunc 5 minute interval in PostgreSQL [duplicate]

SELECT date_trunc('hour', date1) AS hour_stump
     , (extract(minute FROM date1)::int / 5) AS min5_slot
     , count(*)
FROM   table1
GROUP  BY 1, 2
ORDER  BY 1, 2;

You could GROUP BY two columns: a timestamp truncated to the hour and a 5-minute-slot.

The example produces slots 0 - 11. Add 1 if you prefer 1 - 12.
I cast the result of extract() to integer, so the division / 5 truncates fractional digits. The result:
minute 0 – 4 -> slot 0
minute 5 – 9 -> slot 1
etc.

This query only returns values for those 5-minute slots where values are found. If you want a value for every slot or if you want a running sum over 5-minute slots, consider this related answer:

• PostgreSQL: running count of rows for a query ‘by minute’