OLAP 操作：GROUPING SETS

用 SQL 进行数据驱动决策

Irene Ortner

Data Scientist at Applied Statistics

SQL 中的 OLAP 运算符概览

用于支持 OLAP 操作的 SQL 扩展

GROUP BY CUBE
GROUP BY ROLLUP
GROUP BY GROUPING SETS

表 renting_extended

renting_extended 表的前几行：

| renting_id | country  | genre  | rating |
|------------|----------|--------|--------|
| 2          | Belgium  | Drama  | 10     |
| 32         | Belgium  | Drama  | 10     |
| 203        | Austria  | Drama  | 6      |
| 292        | Austria  | Comedy | 8      |
| 363        | Belgium  | Drama  | 7      |
| .......... | ........ | ...... | ...... |

GROUP BY GROUPING SETS

使用 GROUPING SETS 的查询示例：

SELECT country, 
       genre, 
       COUNT(*)
FROM rentings_extended
GROUP BY GROUPING SETS ((country, genre), (country), (genre), ());

用圆括号包裹的列名表示一层聚合。
GROUP BY GROUPING SETS 返回多个 GROUP BY 查询的 UNION。

GROUPING SETS 与 GROUP BY 查询

SELECT country, 
       genre, 
       COUNT(*)
FROM renting_extended
GROUP BY GROUPING SETS (country, genre);

按国家与类型的唯一组合统计租赁数。
GROUPING SETS 中的表达式：(country, genre)

SELECT country, 
       genre, 
       COUNT(*)
FROM renting_extended
GROUP BY country, genre;

| country | genre  | count  |
|---------|--------|--------|
| Austria | Comedy | 2      |
| Belgium | Drama  | 15     |
| Austria | Drama  | 4      |
| Belgium | Comedy | 1      |

GROUPING SETS 与 GROUP BY 查询

SELECT country, COUNT(*)
FROM renting_extended
GROUP BY GROUPING SETS (country);

按国家统计电影租赁数。
GROUPING SETS 中的表达式：(country)

SELECT country, COUNT(*)
FROM renting_extended
GROUP BY country;

| country | count |
|---------|-------|
| Austria | 16    |
| Belgium | 6     |

GROUPING SETS 与 GROUP BY 查询

SELECT genre, COUNT(*)
FROM renting_extended
GROUP BY GROUPING SETS (genre);

按类型统计电影租赁数。
GROUPING SETS 中的表达式：(genre)

SELECT genre, COUNT(*)
FROM renting_extended
GROUP BY genre;

| country | count |
|---------|-------|
| Comedy  | 3     |
| Drama   | 19    |

GROUPING SETS 与 GROUP BY 查询

SELECT COUNT(*)
FROM renting_extended
GROUP BY GROUPING SETS ();

总聚合：统计全部电影租赁数。
GROUPING SETS 中的表达式：()

SELECT COUNT(*)
FROM renting_extended;

| count |
|-------|
| 22    |

GROUP BY GROUPING SETS 记法

GROUP BY GROUPING SETS (...)

SELECT country, genre, COUNT(*)
FROM renting_extended
GROUP BY GROUPING SETS ((country, genre), (country), (genre), ());

对前 4 个查询做 UNION。
在一条查询中汇总数据透视表的全部信息。
等价于 GROUP BY CUBE (country, genre)。

使用 GROUPING SETS 的结果

SELECT country, genre, COUNT(*)
FROM renting_extended
GROUP BY GROUPING SETS ((country, genre), (country), (genre), ());

| country | genre  |count|
|---------|--------|-----|
| NULL    | NULL   | 22  |
| Austria | Comedy | 2   |
| Belgium | Drama  | 15  |
| Austria | Drama  | 4   |
| Belgium | Comedy | 1   |
| Belgium | NULL   | 16  |
| Austria | NULL   | 6   |
| NULL    | Comedy | 3   |
| NULL    | Drama  | 19  |

计算租赁次数与平均评分

仅组合选定的聚合：
- country 与 genre
- genre

使用租赁次数与平均评分聚合。

SELECT country, 
     genre, 
     COUNT(*), 
     AVG(rating) AS avg_rating
FROM renting_extended
GROUP BY GROUPING SETS ((country, genre), (genre));

计算租赁次数与平均评分

SELECT country, genre, COUNT(*), AVG(rating) AS avg_rating
FROM renting_extended
GROUP BY GROUPING SETS ((country, genre), (genre));

| country | genre  | count| avg_rating |
|---------|--------|------|------------|
| Austria | Comedy | 2    | 8.00       |
| Belgium | Drama  | 15   | 9.17       |
| Austria | Drama  | 4    | 6.00       |
| Belgium | Comedy | 1    | NULL       |
| NULL    | Comedy | 3    | 8.00       |
| NULL    | Drama  | 19   | 8.38       |

Passons à la pratique !

用 SQL 进行数据驱动决策