hadoop的mapreduce初级的几个小案例，包括单词计数、topk、单表关联、多表关联、数据排序、数据去重、数据分组，适合刚接触hadoop的人弄清mapreduce的流程- The primary hadoop mapreduce several small cases, including word count, topk, single-table association, multi-table association, data sorting, data deduplica