针对timestamp数据，可以使用DATE_TRUNC或者DATE_PART来截取时间元素。
DATE_TRUNC
https://blog.modeanalytics.com/date-trunc-sql-timestamp-function-count-on/
SELECT DATE_TRUNC('day', occurred_at) AS day,
user_id
FROM benn.fake_fact_events
WHERE event_name = 'complete_signup'
AND occurred_at >= '2014-03-10'
AND occurred_at <= '2014-05-26'
ORDER BY 1 DESC
DATE_PART
http://www.postgresqltutorial.com/postgresql-date_part/
SELECT DATE_PART('dow', occurred_at) day_of_week,
SUM(total) total_qty
FROM orders
GROUP BY 1
ORDER BY 2 DESC;
