cautionary tale vs fairy tale

cautionary tale

noun
  • A story, originally told in folklore, to warn its audience of a certain danger. 

fairy tale

noun
  • A folktale featuring fairies or similar fantasy characters. 

  • A delightful and ideal situation of a kind attained by very few. 

  • A story presented as true that is not believable. 

How often have the words cautionary tale and fairy tale occurred in a corpus of books? (source: Google Ngram Viewer )