gistfile1.txt

[8] pry(main)> Activity.group(:product_id).order(created_at: :desc)
  Activity Load (1.1ms)  SELECT "activities".* FROM "activities"  GROUP BY product_id  ORDER BY "activities"."created_at" DESC
PG::GroupingError: ERROR:  column "activities.id" must appear in the GROUP BY clause or be used in an aggregate function
LINE 1: SELECT "activities".* FROM "activities"  GROUP BY product_id...
               ^
: SELECT "activities".* FROM "activities"  GROUP BY product_id  ORDER BY "activities"."created_at" DESC