Rails & Postgresql: how to group queries by hour?

Question

How do I group by hour in Postgres & Rails? I've read through quite a few SO answers but I'm getting errors.

This works when grouping by date:

Model.group("date(updated_at)").count

Then I tried the following for hour but they didn't work:

Model.group("hour(updated_at)").count
Model.group("date_format(updated_at, '%H')").count
Model.group("extract(hour from updated_at)").count

Once I've found certain hours I need to update, how would I then get the models with those hours? I.e:

Model.where("hour(updated_at) = ?", 5)

Answer 1

You could try the following

Model.group("DATE_PART('hour', updated_at)").count

UPDATE:

How to find records

Model.where("DATE_PART('hour', updated_at) = ?", 5)