You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: 20181207112600_create_check_to_keep_unique_descriptive_exams.rb
    path of file: ./repos/i-diario/db/migrate
    
    the code of the file until where you have to start completion: class CreateCheckToKeepUniqueDes
    
  def change
    execute <<-SQL
      ALTER TABLE descriptive_exams
      ADD CONSTRAINT check_descriptive_exam_is_unique
      CHECK (check_descriptive_exam_is_unique(id, classroom_id, discipline_id, recorded_at)) NOT VALID;
    SQL
  end