rails model migration index code example

Example 1: how do I add index's to a migration in rails

rails generate migration AddUser_idColumnToTable user_id:string. 

class AddIndexToTable < ActiveRecord::Migration
  def change
    add_index :table, :user_id
  end
end

Example 2: how to create an SQL table in ruby

def self.create_table
    sql = <<-SQL
      CREATE TABLE IF NOT EXISTS students (
        name TEXT,
        grade TEXT
      )
    SQL
    DB[:conn].execute(sql)
  end