How to show SQL queries run in the Rails console?

Question

Rails 3+

Enter this line in the console:

ActiveRecord::Base.logger = Logger.new(STDOUT)

Rails 2

Enter this line in the console:

ActiveRecord::Base.connection.instance_variable_set :@logger, Logger.new(STDOUT)

In Rails 3+ you can use ActiveRecord::Relation’s to_sql method:

User.where(:id => 3).to_sql
#=> "SELECT \"users\".* FROM \"users\"  WHERE \"users\".\"id\" = 3"

There is the .explain method in Rails 4.
(.to_sql works too, but won't show includes)

Category.includes(:products).explain
=> EXPLAIN for: SELECT "categories".* FROM "categories" 0|0|0|SCAN TABLE categories

EXPLAIN for: SELECT "categories_products".* FROM "categories_products" WHERE "categories_products"."category_id" IN (1, 2) 0|0|0|SCAN TABLE categories_products

EXPLAIN for: SELECT "products".* FROM "products" WHERE "products"."id" IN (1, 2, 3, 4, 5, 6, 7) 0|0|0|SEARCH TABLE products USING INTEGER PRIMARY KEY (rowid=?) 0|0|0|EXECUTE LIST SUBQUERY 1

Starting from Rails 6 there is more convenient approach: simply add ActiveRecord::Base.verbose_query_logs = true in console and you will see all SQL calls and places where it was called. More info https://guides.rubyonrails.org/debugging_rails_applications.html#verbose-query-logs

As from recently, you can use this:

https://github.com/dejan/rails_panel

It consists of developer console panel add-on for chrome, and gem file which needs to be added to your application's Gemfile like this:

group :development do
  gem 'meta_request'
end

Then run again:

bundle install

Restart your application, open it, and launch developer console, and you should see it like this: