Which shipping agent shipped the most documents? List the shipping agent name and the number of documents.
return shipping agent  ;return documents  shipped ;return number of  #2 for each  #1 ;return #1 where #3 is  highest ;return highest of  #3 ;return names of  #4 ;return #6 ,  #5
['select', 'select', 'group', 'superlative', 'aggregate', 'project', 'union']