比如查某个部门购买的哪些商品是所有部门都没有买过的，这个需要嵌套select吗？
select distinct(item) from table where item not in (select distinct(item) from table where bumen<>'mouge') and bumen='mouge' -----------------不知道对不对......等待实践检验
select * from something where name in (select name from something group by name having COUNT(*)>1)