相关嵌套查询

用 SQL 进行数据驱动决策

Bart Baesens

Professor Data Science and Analytics

相关查询

  • 位于内层查询 WHERE 子句中的条件。
  • 引用外层查询中某个表的列。
用 SQL 进行数据驱动决策

相关查询示例

  • 电影租赁次数大于 5
    SELECT *
FROM movies as m
WHERE 5 < 
  (SELECT COUNT(*)
  FROM renting as r
  WHERE r.movie_id=m.movie_id);
用 SQL 进行数据驱动决策

求值内层查询

SELECT COUNT(*)
FROM renting as r
WHERE r.movie_id = 1;

| count |
|-------|
| 8     |
用 SQL 进行数据驱动决策

求值外层查询

电影租赁次数大于 5

SELECT *
FROM movies as m
WHERE 5 < 
    (SELECT COUNT(*)
    FROM renting as r
    WHERE r.movie_id = m.movie_id);

| movie_id | title                 | genre  | runtime | year_of_release | renting_price |
|----------|-----------------------|--------|---------|-----------------|---------------|
| 1        | One Night at McCool's | Comedy | 93      | 2001            | 2.09          |
| 2        | Swordfish             | Drama  | 99      | 2001            | 2.19          |
用 SQL 进行数据驱动决策

少于 5 次租赁的电影

选择租赁次数小于 5 的电影。

SELECT *
FROM movies as m
WHERE 5 > 
    (SELECT COUNT(*)
    FROM renting as r
    WHERE r.movie_id = m.movie_id);

| movie_id | title           | genre              | runtime | year_of_release | renting_price |
|----------|-----------------|--------------------|---------|-----------------|---------------|
| 17       | The Human Stain | Mystery & Suspense | 106     | 2003            | 1.99          |
| 20       | Love Actually   | Comedy             | 135     | 2003            | 2.29          |
用 SQL 进行数据驱动决策

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用 SQL 进行数据驱动决策

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