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對于經常需要對數據進行多維度的聚合分析的場景，您既需要對A列做聚合，也要對B列做聚合，同時要對A、B兩列做聚合，因此需要多次使用union all。您可以使用grouping sets快速解決此類問題。本文為您介紹如何使用grouping sets進行多維聚合。

功能介紹

grouping sets是對select語句中group by子句的擴展，允許您采用多種方式對結果分組，而不必使用多個select語句再union all來實現。這樣能夠使MaxCompute的引擎給出更有效的執行計劃，從而提高執行性能。

與grouping sets相關聯的語法如下。

類型	說明
`cube`	特殊的`grouping sets`，將指定列的所有可能組合作為`grouping sets`，也可以與`grouping sets`組合使用。 `group by cube (a, b, c) --等效于以下語句。 grouping sets ((a,b,c),(a,b),(a,c),(b,c),(a),(b),(c),()) group by cube ( (a, b), (c, d) ) --等效于以下語句。 grouping sets ( ( a, b, c, d ), ( a, b ), ( c, d ), ( ) ) group by a, cube (b, c), grouping sets ((d), (e)) --等效于以下語句。 group by grouping sets ( (a, b, c, d), (a, b, c, e), (a, b, d), (a, b, e), (a, c, d), (a, c, e), (a, d), (a, e) )`
`rollup`	特殊的`grouping sets`，以按層級聚合的方式產生`grouping sets`，也可以與`grouping sets`組合使用。 `group by rollup (a, b, c) --等效價于以下語句。 grouping sets ((a,b,c),(a,b),(a), ()) group by rollup ( a, (b, c), d ) --等效于以下語句。 grouping sets ( ( a, b, c, d ), ( a, b, c ), ( a ), ( ) ) group by grouping sets((b), (c), rollup(a,b,c)) --等效于以下語句。 group by grouping sets ( (b), (c), (a,b,c), (a,b), (a), () )`
`grouping`	`grouping sets`結果中使用NULL充當占位符，導致您會無法區分占位符NULL與數據中真正的NULL。因此，MaxCompute為您提供了`grouping`。`grouping`接受一個列名作為參數，如果結果對應行使用了參數列做聚合，返回0，此時意味著NULL來自輸入數據。否則返回1，此時意味著NULL是`grouping sets`的占位符。
`grouping_id`	接受一個或多個列名作為參數。結果是將參數列的`grouping`結果按照Bitmap的方式組成整數。
`grouping__id`	`grouping__id`不帶參數，用于兼容Hive查詢。此表達方式在MaxCompute中等價于`grouping_id(group by參數列表)`，參數與`group by`的順序一致。說明 MaxCompute和Hive 2.3.0及以上版本兼容該函數，在Hive 2.3.0以下版本中該函數輸出不一致，因此并不推薦您使用此函數。

GROUPING SETS使用示例

grouping sets使用示例如下：

準備數據。

create table requests lifecycle 20 as 
select * from values 
    (1, 'windows', 'PC', 'Beijing'),
    (2, 'windows', 'PC', 'Shijiazhuang'),
    (3, 'linux', 'Phone', 'Beijing'),
    (4, 'windows', 'PC', 'Beijing'),
    (5, 'ios', 'Phone', 'Shijiazhuang'),
    (6, 'linux', 'PC', 'Beijing'),
    (7, 'windows', 'Phone', 'Shijiazhuang') 
as t(id, os, device, city);

對數據進行分組。您可以通過如下兩種方式進行分組：

使用多個select語句進行分組。

select NULL, NULL, NULL, count(*)
from requests
union all
select os, device, NULL, count(*)
from requests group by os, device
union all
select null, null, city, count(*)
from requests group by city;

使用grouping sets進行分組。

select os,device, city ,count(*)
from requests
group by grouping sets((os, device), (city), ());

返回結果如下：

+------------+------------+------------+------------+
| os         | device     | city       | _c3        |
+------------+------------+------------+------------+
| NULL       | NULL       | NULL       | 7          |
| NULL       | NULL       | Beijing    | 4          |
| NULL       | NULL       | Shijiazhuang | 3          |
| ios        | Phone      | NULL       | 1          |
| linux      | PC         | NULL       | 1          |
| linux      | Phone      | NULL       | 1          |
| windows    | PC         | NULL       | 3          |
| windows    | Phone      | NULL       | 1          |
+------------+------------+------------+------------+

說明

分組集中不使用的表達式，會使用NULL充當占位符，使得這些結果集可以做操作。例如結果第4~8行的city列。

CUBE | ROLLUP使用示例

基于grouping sets示例表，cube及rollup使用示例如下：

示例1：通過cube枚舉os、device、city的所有可能列為grouping sets。命令示例如下：

select os,device, city, count(*)
from requests 
group by cube (os, device, city);
--等效于如下語句。
select os,device, city, count(*)
from requests 
group by grouping sets ((os, device, city),(os, device),(os, city),(device,city),(os),(device),(city),());

返回結果如下：

+------------+------------+------------+------------+
| os         | device     | city       | _c3        |
+------------+------------+------------+------------+
| NULL       | NULL       | NULL       | 7          |
| NULL       | NULL       | Beijing    | 4          |
| NULL       | NULL       | Shijiazhuang | 3          |
| NULL       | PC         | NULL       | 4          |
| NULL       | PC         | Beijing    | 3          |
| NULL       | PC         | Shijiazhuang | 1          |
| NULL       | Phone      | NULL       | 3          |
| NULL       | Phone      | Beijing    | 1          |
| NULL       | Phone      | Shijiazhuang | 2          |
| ios        | NULL       | NULL       | 1          |
| ios        | NULL       | Shijiazhuang | 1          |
| ios        | Phone      | NULL       | 1          |
| ios        | Phone      | Shijiazhuang | 1          |
| linux      | NULL       | NULL       | 2          |
| linux      | NULL       | Beijing    | 2          |
| linux      | PC         | NULL       | 1          |
| linux      | PC         | Beijing    | 1          |
| linux      | Phone      | NULL       | 1          |
| linux      | Phone      | Beijing    | 1          |
| windows    | NULL       | NULL       | 4          |
| windows    | NULL       | Beijing    | 2          |
| windows    | NULL       | Shijiazhuang | 2          |
| windows    | PC         | NULL       | 3          |
| windows    | PC         | Beijing    | 2          |
| windows    | PC         | Shijiazhuang | 1          |
| windows    | Phone      | NULL       | 1          |
| windows    | Phone      | Shijiazhuang | 1          |
+------------+------------+------------+------------+

示例2：通過cube枚舉(os, device),(device, city)所有可能列為grouping sets。命令示例如下：

select os,device, city, count(*) 
from requests 
group by cube ((os, device), (device, city));
--等效于如下語句。
select os,device, city, count(*) 
from requests 
group by grouping sets ((os, device, city),(os, device),(device,city),());

返回結果如下：

+------------+------------+------------+------------+
| os         | device     | city       | _c3        |
+------------+------------+------------+------------+
| NULL       | NULL       | NULL       | 7          |
| NULL       | PC         | Beijing    | 3          |
| NULL       | PC         | Shijiazhuang | 1          |
| NULL       | Phone      | Beijing    | 1          |
| NULL       | Phone      | Shijiazhuang | 2          |
| ios        | Phone      | NULL       | 1          |
| ios        | Phone      | Shijiazhuang | 1          |
| linux      | PC         | NULL       | 1          |
| linux      | PC         | Beijing    | 1          |
| linux      | Phone      | NULL       | 1          |
| linux      | Phone      | Beijing    | 1          |
| windows    | PC         | NULL       | 3          |
| windows    | PC         | Beijing    | 2          |
| windows    | PC         | Shijiazhuang | 1          |
| windows    | Phone      | NULL       | 1          |
| windows    | Phone      | Shijiazhuang | 1          |
+------------+------------+------------+------------+

示例3：通過rollup對os、device、city以按層級聚合的方式產生grouping sets。命令示例如下：

select os,device, city, count(*)
from requests 
group by rollup (os, device, city);
--等效于如下語句。
select os,device, city, count(*)
from requests 
group by grouping sets ((os, device, city),(os, device),(os),());

返回結果如下：

+------------+------------+------------+------------+
| os         | device     | city       | _c3        |
+------------+------------+------------+------------+
| NULL       | NULL       | NULL       | 7          |
| ios        | NULL       | NULL       | 1          |
| ios        | Phone      | NULL       | 1          |
| ios        | Phone      | Shijiazhuang | 1          |
| linux      | NULL       | NULL       | 2          |
| linux      | PC         | NULL       | 1          |
| linux      | PC         | Beijing    | 1          |
| linux      | Phone      | NULL       | 1          |
| linux      | Phone      | Beijing    | 1          |
| windows    | NULL       | NULL       | 4          |
| windows    | PC         | NULL       | 3          |
| windows    | PC         | Beijing    | 2          |
| windows    | PC         | Shijiazhuang | 1          |
| windows    | Phone      | NULL       | 1          |
| windows    | Phone      | Shijiazhuang | 1          |
+------------+------------+------------+------------+

示例4：通過rollup對os, (os,device), city以按層級聚合的方式產生grouping sets。命令示例如下：

select os,device, city, count(*)
from requests 
group by rollup (os, (os,device), city);
--等效于如下語句。
select os,device, city, count(*)
from requests 
group by grouping sets ((os, device, city),(os, device),(os),());

返回結果如下：

+------------+------------+------------+------------+
| os         | device     | city       | _c3        |
+------------+------------+------------+------------+
| NULL       | NULL       | NULL       | 7          |
| ios        | NULL       | NULL       | 1          |
| ios        | Phone      | NULL       | 1          |
| ios        | Phone      | Shijiazhuang | 1          |
| linux      | NULL       | NULL       | 2          |
| linux      | PC         | NULL       | 1          |
| linux      | PC         | Beijing    | 1          |
| linux      | Phone      | NULL       | 1          |
| linux      | Phone      | Beijing    | 1          |
| windows    | NULL       | NULL       | 4          |
| windows    | PC         | NULL       | 3          |
| windows    | PC         | Beijing    | 2          |
| windows    | PC         | Shijiazhuang | 1          |
| windows    | Phone      | NULL       | 1          |
| windows    | Phone      | Shijiazhuang | 1          |
+------------+------------+------------+------------+

示例5：通過group by、cube、grouping sets組合產生grouping sets。命令示例如下：

select os,device, city, count(*)
from requests 
group by os, cube(os,device), grouping sets(city);
--等效于如下語句。
select os,device, city, count(*)
from requests 
group by grouping sets((os,device,city),(os,city),(os,device,city));

返回結果如下：

+------------+------------+------------+------------+
| os         | device     | city       | _c3        |
+------------+------------+------------+------------+
| ios        | NULL       | Shijiazhuang | 1          |
| ios        | Phone      | Shijiazhuang | 1          |
| linux      | NULL       | Beijing    | 2          |
| linux      | PC         | Beijing    | 1          |
| linux      | Phone      | Beijing    | 1          |
| windows    | NULL       | Beijing    | 2          |
| windows    | NULL       | Shijiazhuang | 2          |
| windows    | PC         | Beijing    | 2          |
| windows    | PC         | Shijiazhuang | 1          |
| windows    | Phone      | Shijiazhuang | 1          |
+------------+------------+------------+------------+

GROUPING | GROUPING_ID使用示例

grouping及grouping_id使用示例如下：

select a,b,c,count(*),
grouping(a) ga, grouping(b) gb, grouping(c) gc, grouping_id(a,b,c) groupingid 
from values (1,2,3) as t(a,b,c)
group by cube(a,b,c);

返回結果如下：

+------------+------------+------------+------------+------------+------------+------------+------------+
| a          | b          | c          | _c3        | ga         | gb         | gc         | groupingid |
+------------+------------+------------+------------+------------+------------+------------+------------+
| NULL       | NULL       | NULL       | 1          | 1          | 1          | 1          | 7          |
| NULL       | NULL       | 3          | 1          | 1          | 1          | 0          | 6          |
| NULL       | 2          | NULL       | 1          | 1          | 0          | 1          | 5          |
| NULL       | 2          | 3          | 1          | 1          | 0          | 0          | 4          |
| 1          | NULL       | NULL       | 1          | 0          | 1          | 1          | 3          |
| 1          | NULL       | 3          | 1          | 0          | 1          | 0          | 2          |
| 1          | 2          | NULL       | 1          | 0          | 0          | 1          | 1          |
| 1          | 2          | 3          | 1          | 0          | 0          | 0          | 0          |
+------------+------------+------------+------------+------------+------------+------------+------------+

默認情況，group by列表中不被使用的列，會被填充為NULL。您可以通過grouping輸出更有實際意義的值。基于grouping sets示例表，命令示例如下：

select
  if(grouping(os) == 0, os, 'ALL') as os,
  if(grouping(device) == 0, device, 'ALL') as device,
  if(grouping(city) == 0, city, 'ALL') as city, 
  count(*) as count 
from requests 
group by os, device, city grouping sets((os, device), (city), ());

返回結果如下：

+------------+------------+------------+------------+
| os         | device     | city       | count      |
+------------+------------+------------+------------+
| ALL        | ALL        | ALL        | 7          |
| ALL        | ALL        | Beijing    | 4          |
| ALL        | ALL        | Shijiazhuang | 3          |
| ios        | Phone      | ALL        | 1          |
| linux      | PC         | ALL        | 1          |
| linux      | Phone      | ALL        | 1          |
| windows    | PC         | ALL        | 3          |
| windows    | Phone      | ALL        | 1          |
+------------+------------+------------+------------+

GROUPING__ID使用示例

grouping__id不帶參數的命令示例如下：

set odps.sql.hive.compatible=true;
select      
a, b, c, count(*), grouping__id 
from values (1,2,3) as t(a,b,c) 
group by a, b, c grouping sets ((a,b,c), (a));
--等效于如下語句。
select      
a, b, c, count(*), grouping_id(a,b,c)  
from values (1,2,3) as t(a,b,c) 
group by a, b, c grouping sets ((a,b,c), (a));

返回結果如下：

+------------+------------+------------+------------+------------+
| a          | b          | c          | _c3        | _c4        |
+------------+------------+------------+------------+------------+
| 1          | NULL       | NULL       | 1          | 3          |
| 1          | 2          | 3          | 1          | 0          |
+------------+------------+------------+------------+------------+

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功能介紹

GROUPING SETS使用示例

CUBE | ROLLUP使用示例

GROUPING | GROUPING_ID使用示例

GROUPING__ID使用示例