How many more strikeouts did Johnson have than walks while with the Expos?
return Johnson ;return strikeouts of #1 while with the  Expos ;return walks of #1 while with the  Expos ;return number of  #2 ;return number of  #3 ;return difference of #4 and  #5
['select', 'project', 'project', 'aggregate', 'aggregate', 'arithmetic']