Hive的高级聚合函数

高级聚合
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GROUPING SETS.
group by + union all 

//查询每个cust的订单数
select count(*) from orders group by cid ;
select count(*) from orders group by orderno ;

//group + union all
select count(*) from orders group by cid union all select count(*) from orders group by orderno ;
//group by :指定按照哪些字段分组，
//grouping sets : 以上字段集如何组合。
select count(*) from orders group by cid,orderno grouping sets(cid,orderno,()) 

rollup
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rollup扩展了group by，
rollup比grouping sets多了一层聚合(n + 1)。

GROUP BY a,b,c WITH ROLLUP
GROUP BY a,b,c GROUPING SETS ((a,b,c),(a,b),(a),())

select cid,orderno,count(*) GROUP BY cid,orderno GROUPING SETS ((cid,orderno),(cid),())


cube
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扩展了grouping sets，做了各种条件的组合，不做排序。

等价于
GROUP BY a,b,c GROUPING SETS ((a,b,c),(a,b),(b,c),(a,c),(a),(b),(c),())

聚合条件
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having,用于在组内过滤。
//使用having
select cid , max(price) mx from orders group by cid having mx > 100.1 ; 

//嵌套子查询
select t.cid , t.mx from (select cid , max(price) mx from orders group by cid) t where t.mx > 100.1 ;