SQL查询：聚合具有时间戳字段的记录，其中字段时间戳属于相同的时间单位（秒，分钟，小时..）

Question

I have a database table customers that records among others the arrival time of clients for a one month data. So, the customers table contains among other a column named arrival_time . (eg, arrival_time = 12/1/2020 12:01:39 AM, arrival_time = 12/1/2020 12:01:34 AM etc…) Is it possible to design/write an SQL query that returns the numbers of customers that arrived each second (or say, min, hour...) in this this one month data.

Thank you.

Answer 1

If you are using PostgreSQL you can use DATE_TRUNC() . For example:

select
  date_trunc('minute', arrival_time) as at,
  count(distinct customer_id) as cnt
from t
group by date_trunc('minute', arrival_time)

You can change 'minute' for 'day' , 'week' , 'second' , etc. See https://www.postgresql.org/docs/current/functions-datetime.html#FUNCTIONS-DATETIME-TRUNC