hive的语句执行顺序是group by ... select ... order by
order by是对前面查询到的结果进行排序，两者连用的语法顺序即 select ... group by ... order by
注意事项有两点：
1. order by的字段必须是在group by中，或者是聚合函数
1. select file1,file2 from tableName group by file1,file2 order by file1; 2. select file1, count(*) as num from tableName group by file1 order by count(*)
2. 写法上，order by后的字段顺序，必须与group by后的字段顺序一致，两者都是从左到右执行，group by A，B，C，执行的时候会先对A列分组，再在每个组里对B进行分组，以此类推
select file1,file2,file3 from tableName group by file1,file2,file3 order by file1,file2;
