Rails (PG::GroupingError: ERROR: column must appear in the GROUP BY clause or be used in an aggregate function

问题

In my local this query work perfect with sqlite3

 def Event.most_like
   select("events.*, count(like_events.event_id) as likes_count")
   .joins(:like_events).group(:event_id).order("likes_count 
    DESC").limit(4)
 end

but i got some error when deploy heroku PG::GroupingError: ERROR: column "events.id" must appear in the GROUP BY clause or be used in an aggregate function

Can someone help me fix this?

回答1:

As the message, all fields in Select clause must appear in the GROUP BY or in aggregate function. In this case, you select all fields of Event so that the fields, which includes events.id, need to satisfy above requirement.

To fix that, I suggest to change function to select only event's id and likes_count as below:

def Event.most_like
  select("events.id, count(like_events.event_id) as likes_count").
  joins(:like_events).
  group('events.id').
  order("likes_count DESC").
  limit(4)
end

If you still need to get event records, you can fetch those records based on their ids.

来源：https://stackoverflow.com/questions/48369349/rails-pggroupingerror-error-column-must-appear-in-the-group-by-clause-or-be