Remove duplicate records based on multiple columns?

Question

I\'m using Heroku to host my Ruby on Rails application and for one reason or another, I may have some duplicate rows.

Is there a way to delete duplicate records base

Answer 1

If your User table data like below

User.all =>
[
    #, 
    #, 
    #, 
    #, 
    #, 
    #] 
1.9.2p290 :099 > 

Email id's are duplicate, so our aim is to remove all duplicate email ids from user table.

Step 1:

To get all distinct email records id.

ids = User.select("MIN(id) as id").group(:email,:name).collect(&:id)
=> [15, 16, 18, 19, 17]

Step 2:

To remove duplicate id's from user table with distinct email records id.

Now the ids array holds the following ids.

[15, 16, 18, 19, 17]
User.where("id NOT IN (?)",ids)  # To get all duplicate records
User.where("id NOT IN (?)",ids).destroy_all

** RAILS 4 **

ActiveRecord 4 introduces the .not method which allows you to write the following in Step 2:

User.where.not(id: ids).destroy_all