按客户的花费（子查询）

用 SQL 进行数据驱动决策

Tim Verdonck

Professor Statistics and Data Science

后续 SELECT 语句——女演员

查询 1：

SELECT *
FROM actors
WHERE gender = 'female';

| actor_id | name          | year_of_birth | nationality | gender |
|----------|---------------|---------------|-------------|--------|
| 1        | Abbie Cornish | 1982          | Australia   | female |
| 4        | Amy Adams     | 1974          | USA         | female |

后续 SELECT 语句——女演员

SELECT * -- Query 1
FROM actors
WHERE gender = 'female';

按国籍对查询 1 的结果分组。
给出各国最年长与最年轻女演员的出生年份。

SELECT af.nationality, 
       MIN(af.year_of_birth), 
       MAX(af.year_of_birth)
FROM
    (SELECT *
    FROM actors
    WHERE gender = 'female') AS af
GROUP BY af.nationality;

后续 SELECT 结果——女演员

SELECT af.nationality, 
       MIN(af.year_of_birth), 
       MAX(af.year_of_birth)
FROM
    (SELECT *
    FROM actors
    WHERE gender = 'female') AS af
GROUP BY af.nationality;

| nationality | min  | max  |
|-------------|------|------|
| Italy       | 1976 | 1976 |
| Iran        | 1952 | 1952 |
| USA         | 1945 | 1993 |

每位客户花了多少钱？

第一步：将 movies 中的 renting_price 加入 renting 表。

SELECT r.customer_id,
       m.renting_price
FROM renting AS r
LEFT JOIN movies AS m
ON r.movie_id=m.movie_id;

| customer_id | renting_price |
|-------------|---------------|
| 41          | 2.59          |
| 10          | 2.79          |
| 108         | 2.39          |
| 39          | 1.59          |
| 104         | 1.69          |

每位客户花了多少钱？

第二步：
- 按 customer_id 对第一步结果分组
- 求 renting_price 的合计

SELECT rm.customer_id, 
           SUM(rm.renting_price)
FROM
       (SELECT r.customer_id, 
               m.renting_price
       FROM renting AS r
       LEFT JOIN movies AS m
       ON r.movie_id=m.movie_id) AS rm
GROUP BY rm.customer_id;

每位客户花了多少钱？

| customer_id | sum   |
|-------------|-------|
| 116         | 7.47  |
| 87          | 17.53 |
| 71          | 6.87  |
| 68          | 1.59  |
| 51          | 4.87  |

Vamos praticar!

用 SQL 进行数据驱动决策