ruby.rb

  def validate()
    balance = @mysql.query("SELECT Balance FROM Balance WHERE AccountID = #{@sender_id} ORDER BY Date DESC LIMIT 1")
    if balance >= @amount
      return true
    else
      return false
    end
  end

  # Esegue il bonifico con una query MySQL
  def do()
    if self.validate
      @mysql.query("CALL Transfer(#{@sender_id}, #{@recipient_id}, #{@amount})")
    end
  end

Rather than the whole if statement with return true and return false just:

balance >= @amount