How many workers did the labor force drop by between 2006 and 2007?
return the  labor force ;return workers of #1 ;return #2 in  2006 ;return #2 in  2007 ;return number of  #3 ;return number of  #4 ;return difference of #5 and  #6
['select', 'project', 'filter', 'filter', 'aggregate', 'aggregate', 'arithmetic']