DateTime arithmetic in an ActiveRecord query (PostgreSQL)

Question

I have two datetime columns in a User/users table: created_at and birthdate. I\'d like to find users whose b

Answer 1

The easiest way to do this is to use an interval, then it is pretty much a straight transliteration of the Rails version:

User.where(%q{created_at - birthdate < interval '13 years'})

The difference between two timestamps (or a timestamp and a date) is an interval so you just need the appropriate value on the right side of your comparison.

Answer 2

You simply have to formulate that in PostgreSQL syntax inside your where clause.

For MySQL this would look similar to this using the datediff function:

User.where("DATEDIFF(created_at, birthdate) > (13 * 365)")

13*356 is there to represent 3 years in days since datediff returns difference in days.

I would then encapsulate that in a scope-like function like the following:

class User < ActiveRecord::Model
  def self.age_difference(years)
    where("DATEDIFF(created_at, birthdate) > (? * 365)", years)
  end
end

So you can call it:

User.age_difference(13).each do |user|
  puts user.inspect
end

I guess it's similar in Postgres.