Count entries in postgresql grouped by date

[Linus Pettersson]

Hi!

I have a table with visits with a visited_at: attribute which is a datetime field. They seem to be stored as UTC. Now I want to count all visits each day and return something like:

{

  2013-01-01: 8,

  2013-01-02: 4,

  2013-01-07: 9,

  ...

}

So, I did it like this which kind of works...:

  def self.total_grouped_by_day(start_date, end_date)

    visits = where(visited_at: start_date..end_date)

    visits = visits.group("date(visited_at)")

    visits = visits.select("date(visited_at) as date, count(visits.id) as total_visits")

    visits = visits.order("date ASC")

    visits.group_by { |v| v.date.to_date }

  end

It doesn't return exactly the format I want but that's not the big problem. The problem is that if a visit happens near midnight it may be counted at the "wrong" date due to time zones. I understand why, because "date(visited_at)" doesn't know anything about my timezone.

Any good ideas on how to fix this issue?

[Linus Pettersson]

I'll just don't do the group and count in the database for now. I do it like this instead:

  def self.total_grouped_by_day(start_date, end_date)

    visits = where(visited_at: start_date..end_date)

    visits = visits.order("visited_at ASC")

    visits.group_by { |v| v.visited_at.to_date }

  end

And then just use visits[date].count for the counting. There will probably not be that many records anyway...

[Scott Ribe]

You're looking for the "AT TIME ZONE" construct.

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--
Scott Ribe
scott...@elevated-dev.com
http://www.elevated-dev.com/
(303) 722-0567 voice