code: def create_index(self, cardinality):
          
          for i in reversed(range(cardinality)):
              if i != 0:
                  query = "CREATE INDEX idx_{0}_gram_{1} ON _{0}_gram(word_{1});".format(cardinality, i)
                  self.execute_sql(query)
docs: Create an index for the table with the given cardinality.
  
          Parameters
          ----------
          cardinality : int
              The cardinality to create a index for.