docs: def _init_sqlite_functions(self):
          """additional SQL functions to the database"""
  
          self.connection.create_function("sqrt", 1,sqlfunctions._sqrt)
          self.connection.create_function("sqr", 1,sqlfunctions._sqr)
          self.connection.create_function("periodic", 1,sqlfunctions._periodic)
          self.connection.create_function("pow", 2,sqlfunctions._pow)
          self.connection.create_function("match",2,sqlfunctions._match)
          self.connection.create_function("regexp",2,sqlfunctions._regexp)
          self.connection.create_function("fformat",2,sqlfunctions._fformat)
          self.connection.create_aggregate("std",1,sqlfunctions._Stdev)
          self.connection.create_aggregate("stdN",1,sqlfunctions._StdevN)
          self.connection.create_aggregate("median",1,sqlfunctions._Median)
          self.connection.create_aggregate("array",1,sqlfunctions._NumpyArray)
          self.connection.create_aggregate("histogram",4,sqlfunctions._NumpyHistogram)
          self.connection.create_aggregate("distribution",4,sqlfunctions._NormedNumpyHistogram)
          self.connection.create_aggregate("meanhistogram",5,sqlfunctions._MeanHistogram)
          self.connection.create_aggregate("stdhistogram",5,sqlfunctions._StdHistogram)
          self.connection.create_aggregate("minhistogram",5,sqlfunctions._MinHistogram)
          self.connection.create_aggregate("maxhistogram",5,sqlfunctions._MaxHistogram)
          self.connection.create_aggregate("medianhistogram",5,sqlfunctions._MedianHistogram)
          self.connection.create_aggregate("zscorehistogram",5,sqlfunctions._ZscoreHistogram)