Question

我正在尝试了解窗口功能avg的工作原理，并且似乎不按我的预期工作。

这是数据集：

select * from winsales;
+-------------------+------------------+--------------------+-------------------+---------------+-----------------------+--+
| winsales.salesid  | winsales.dateid  | winsales.sellerid  | winsales.buyerid  | winsales.qty  | winsales.qty_shipped  |
+-------------------+------------------+--------------------+-------------------+---------------+-----------------------+--+
| 30001             | NULL             | 3                  | b                 | 10            | 10                    |
| 10001             | NULL             | 1                  | c                 | 10            | 10                    |
| 10005             | NULL             | 1                  | a                 | 30            | NULL                  |
| 40001             | NULL             | 4                  | a                 | 40            | NULL                  |
| 20001             | NULL             | 2                  | b                 | 20            | 20                    |
| 40005             | NULL             | 4                  | a                 | 10            | 10                    |
| 20002             | NULL             | 2                  | c                 | 20            | 20                    |
| 30003             | NULL             | 3                  | b                 | 15            | NULL                  |
| 30004             | NULL             | 3                  | b                 | 20            | NULL                  |
| 30007             | NULL             | 3                  | c                 | 30            | NULL                  |
| 30001             | NULL             | 3                  | b                 | 10            | 10                    |
+-------------------+------------------+--------------------+-------------------+---------------+-----------------------+--+

当我触发以下查询->

select salesid, sellerid, qty, avg(qty) over (order by sellerid) as avg_qty from winsales order by sellerid,salesid;

我得到以下内容->

 +----------+-----------+------+---------------------+--+
| salesid  | sellerid  | qty  |       avg_qty       |
+----------+-----------+------+---------------------+--+
| 10001    | 1         | 10   | 20.0                |
| 10005    | 1         | 30   | 20.0                |
| 20001    | 2         | 20   | 20.0                |
| 20002    | 2         | 20   | 20.0                |
| 30001    | 3         | 10   | 18.333333333333332  |
| 30001    | 3         | 10   | 18.333333333333332  |
| 30003    | 3         | 15   | 18.333333333333332  |
| 30004    | 3         | 20   | 18.333333333333332  |
| 30007    | 3         | 30   | 18.333333333333332  |
| 40001    | 4         | 40   | 19.545454545454547  |
| 40005    | 4         | 10   | 19.545454545454547  |
+----------+-----------+------+---------------------+--+

问题是-如何计算avg（qty）。由于我没有使用partition by，因此我希望所有行的avg（qty）都相同。

有什么想法吗？

Answer 1

如果您想让相同的avg（qty）用于所有行，然后在over子句中删除 order by sellerid，那么您将具有<所有行的strong> 19.545454545454547 值。

查询以获取所有行的平均avg（qty）：

hive> select salesid, sellerid, qty, avg(qty) over () as avg_qty from winsales order by sellerid,salesid;

如果我们在 over子句中包含order by sellerid，则您将获得每个卖方ID的累计平均值。即用于

sellerid 1 you are having 2 records total 2 records with qty as 10,30 so avg would be 
     (10+30)/2.
sellerid 2 you are having 2 records total 4 records with qty as 20,20 so avg would be 
     (10+30+20+20)/4 = 20.0
sellerid 3 you are having 5 records total 9 records with qty as  so 10,10,15,20,30 avg would be 
(10+30+20+20+10+10+15+20+30)/9 = 18.333
sellerid 4 avg is 19.545454545454547

当我们包含over子句时，这是蜂巢的预期行为。

Hive中带有-over（按colName排序）的窗口功能avg

1 个答案: