execute raw sql in rails app

ac_raw_sql.rb

class MyMigration < ActiveRecord::Migration
  def up
    create_table :users do
      t.string :name
      t.integer :age
    end
  end
end

MyMigration.migrate(:up) 
# or MyMigration.new.up

# or not using migration
ActiveRecord::Base.connection.instance_eval do
  create_table :users do
    t.string :name
    t.integer :age
  end
end

arel_table = Arel::Table.new(:users)
# insert
insert_arel = arel_table.compile_insert({arel_table[:name] => 'jack', arel_table[:age] => 20})
ActiveRecord::Base.connection.insert(insert_arel)

# select
select_arel = arel_table.project(Arel.sql('*')).take(1)
ActiveRecord::Base.connection.select_one(select_arel)
#result is a hash {id: 1, name: 'jack', age: 20}

count_arel = arel_table.project(Arel.sql('*').count)
ActiveRecord::Base.connection.select_value(select_arel)

distinct_count_arel = arel_table.project(arel_table[:name].count(true))
ActiveRecord::Base.connection.select_value(distinct_count_arel)