How many more passing touchdowns did Marques Colston catch compared to Vernon Davis?
return Marques Colston ;return Vernon Davis ;return touchdown catches of #1 ;return touchdown catches of #2 ;return number of  #3 ;return number of  #4 ;return the  difference of #5 and  #6
['select', 'select', 'project', 'project', 'aggregate', 'aggregate', 'arithmetic']