second string vs unsatisfactory

second string

adj
  • Not as good; of a lower quality or condition. 

noun
  • A unit of players which is considered to have a secondary level of talent and which usually plays after the first string. 

unsatisfactory

adj
  • inadequate, substandard or not satisfactory 

How often have the words second string and unsatisfactory occurred in a corpus of books? (source: Google Ngram Viewer )