how to use DISTINCT ON with mysql using ActiveRecord

Question

Want all the latest visit of all the distinct user.

For this I am using below query

Event.order(time: :desc).select(\'DISTINCT ON(user_id) user_id,          


        

Answer 1

So you want all user visits with last visited time.

Instead of use DISTINCT function, you can use GROUP with MAX function.

Query looks like

Events.group(:user_id).maximum(:time)

This Outputs your desired results

{21=>Tue, 18 Dec 2018 11:15:24 UTC +00:00, 23=>Thu, 20 Dec 2018 06:42:10 UTC +00:00}

Hope this works for you.

FYI DISTINCT ON(columns). is PostgreSQL Syntax.