Rails: must appear in the GROUP BY clause or be used in an aggregate function

Question

I'm following along Bate's tut on graphs & charts but am getting an error.

This is the error I'm getting

PG::Error: ERROR:  column "orders.created_at" must appear in the GROUP BY clause or be used in an aggregate function
LINE 1: SELECT created_at, sum(amount) as total_amount FROM "orders"...
               ^
: SELECT created_at, sum(amount) as total_amount FROM "orders"  WHERE ("orders"."created_at" BETW

And this is the code I'm using in my Orders model

def self.total_grouped_by_day(start)
    orders = where(created_at: start.beginning_of_day..Time.zone.now)#.all
    orders = orders.group("date(created_at)")
    orders = orders.select("date(created_at), sum(amount) as total_amount")
    orders.group_by { |order| order.created_at.to_date }
  end

and in my helper

def orders_chart_data
        orders_by_day = Order.total_grouped_by_day(3.weeks.ago)
        (3.weeks.ago.to_date..Date.today).map do |date|
            {
                created_at: date,
                price: orders_by_day[date].first.try(:total_amount) || 0
            }
        end
    end

---

I'm using Postgres (which I'm pretty sure is the main reason I'm getting this error) & Rails 3.x.x. Why is this error occurring & how do I fix it?

Thank you in advance

---

In my console:

Order.where(created_at: 3.weeks.ago.beginning_of_day..Time.zone.now).group("date(created_at)").select("date(created_at), sum(amount) as total_amount")

& this is what I get

[#<Order >, #<Order >, #<Order >] 

weird..

---

running this in my console: Order.where(created_at: 3.weeks.ago.beginning_of_day..Time.zone.now).group("date(created_at)").select("date(created_at), sum(amount) as total_amount").first.total_amount

gives me this:

Creating scope :page. Overwriting existing method Order.page.
  Order Load (18.1ms)  SELECT date(created_at), sum(amount) as total_amount FROM "orders" WHERE ("orders"."created_at" BETWEEN '2013-07-05 00:00:00.000000' AND '2013-07-26 23:50:38.876609') GROUP BY date(created_at) LIMIT 1
 => "10.0"

Answer 1

You are grouping on date(created_at) but not selecting that column. Change this line:

orders = orders.select("created_at, sum(amount) as total_amount")

to this:

orders = orders.select("date(created_at), sum(amount) as total_amount")

That will also result in a change to the next line's group_by as well.

From one of my projects, using slightly different attributes, but doing the same thing as you:

1.9.3p327 > User.group('date(created_at)').select('date(created_at), sum(id) as total_amount').first.attributes
  User Load (1.2ms)  SELECT date(created_at), sum(id) as total_amount FROM "users" GROUP BY date(created_at) LIMIT 1
 => {"date"=>"2011-09-27", "total_amount"=>"657"}

Answer 2

A cast to date would be simplest & fastest. Here the raw SQL since I am no expert with Ruby syntax (and no fan of ORMs butchering SQL in general).

SELECT created_at::date, sum(amount) AS total_amount
FROM   orders
WHERE  created_at ...
GROUP  BY created_at::date
ORDER  BY created_at::date