hive几种排序

• order by：全局排序
  select * from emp order by sal;

• sort by：对于每个reduce进行排序
  set mapreduce.job.reduces=3;
  insert overwrite local directory ‘/opt/datas/emp_sort’
  row format delimited fields terminated by ‘\t’ select * from emp sort by sal;

• distribute by :底层就是mapreduce 的分区，一般与sort by连用
  insert overwrite local directory ‘/opt/datas/emp_dis’
  row format delimited fields terminated by ‘\t’
  select * from emp distribute by deptno sort by sal;

• cluster by:等价于distribute by 与sort by的字段相同时
  insert overwrite local directory ‘/opt/datas/emp_cls’
  row format delimited fields terminated by ‘\t’
  select * from emp cluster by sal;