With Rails, how can I query the db for an aggregate number and grouped by week?

问题

Given a table like so:

Log:

id, user_id, points, created_at

With Rails, how can I query the database by user_id and then GROUPED by week via created_at where I can then having something like:

   WEEK of X/XX/XXXX - 3011 total points
   WEEK of X/XX/XXXX - 320 total points
   WEEK of X/XX/XXXX - 31 total points
   WEEK of X/XX/XXXX - 30330 total points

Thanks

回答1:

points_by_week = Log.where(user_id: user_id).group("DATE_TRUNC('year', created_at)", "DATE_TRUNC('week', created_at)").sum(:points)

Will yield a result like

{[2014, 4]=>3,
 [2014, 8]=>7,
 [2015, 4]=>26,
 [2015, 6]=>19,
 [2015, 12]=>50,
 [2015, 32]=>48,
 [2016, 2]=>78,
 [2016, 3]=>45,
 [2016, 4]=>49,
 [2016, 5]=>110,
 [2016, 45]=>30,
 [2017, 4]=>130,
 [2017, 11]=>185}

where the key is [year, week], then you can use Date.commercial to get the week of

points_by_week.each do |(year, week), count|
  date = Date.commercial(year, week)
  puts "Week of #{date.strftime('%d/%m/%Y')} - #{count} total points"
end

And (just cause I can), the mysql version of the query looks like this

points_by_week = Log.where(user_id: user_id).group("year(created_at)", "week(created_at)").sum(:points)

This by default assumes the week starts on Monday, and the first week of a year is starts on the first Monday of the year

回答2:

something like:

points_by_week = Log.select("DATE_TRUNC('week', created_at) as week, sum(points) as total_points").group("week").where(user_id: x)

points_by_week.each do |pw|
  puts "Week of #{pw.week.strftime('%d/%m/%Y')} - #{pw.total_points} total points"
end

EDIT

as per Michael Gorman comment the above won't distinguish between years (2017, 2016, etc), so you might need to group by week and year depending on your requirements:

Log.select("DATE_TRUNC('week', created_at) as week, DATE_TRUNC('year', created_at) as year, sum(points) as total_points").group("week, year")

and you can keep using the above loop to display it ;)

回答3:

Something like this:

select 'WEEK of ' || TO_CHAR(date_trunc( 'week', created_at ), 'dd/mm/yyyy') || ' - ' || sum(points) || ' total points'
FROM clients
  WHERE id < 100000
  GROUP BY date_trunc( 'week', created_at );

|| is used to concatenate string.

TO_CHAR is used as a data type formatting functions.

来源：https://stackoverflow.com/questions/44657770/with-rails-how-can-i-query-the-db-for-an-aggregate-number-and-grouped-by-week