巢狀查詢

以資料驅動的 SQL 決策制定

Irene Ortner

Data Scientist at Applied Statistics

巢狀查詢

在 WHERE 或 HAVING 子句中的 SELECT 區塊
內層查詢回傳單一或多個值
用內層查詢結果在另一個查詢中篩選特定列

內層查詢

步驟 1：內層查詢

SELECT DISTINCT customer_id
FROM renting
WHERE rating <= 3

| customer_id |
|-------------|
| 28          |
| 41          |
| 86          |
| 120         |

在 WHERE 子句中的結果

SELECT name
FROM customers
WHERE customer_id IN (28, 41, 86, 120);

外層查詢

步驟 2：外層查詢

SELECT name
FROM customers
WHERE customer_id IN
    (SELECT DISTINCT customer_id
    FROM renting
    WHERE rating <= 3);

| name            |
|-----------------|
| Sidney Généreux |
| Zara Mitchell   |

在 HAVING 子句中的巢狀查詢

步驟 1：內層查詢

SELECT MIN(date_account_start)
FROM customers
WHERE country = 'Austria';

| min        |
|------------|
| 2017-11-22 |

在 HAVING 子句中的巢狀查詢

步驟 2：外層查詢

SELECT country, MIN(date_account_start)
FROM customers
GROUP BY country
HAVING MIN(date_account_start) <
    (SELECT MIN(date_account_start)
    FROM customers
    WHERE country = 'Austria');

| country       | min        |
|---------------|------------|
| Spain         | 2017-02-14 |
| Great Britain | 2017-03-31 |

電影「Ray」有哪些演員？

SELECT name
FROM actors
WHERE actor_id IN
    (SELECT actor_id 
     FROM actsin
     WHERE movie_id =
        (SELECT movie_id 
         FROM movies
         WHERE title='Ray'));

| name             |
|------------------|
| Jamie Foxx       |
| Kerry Washington |
| Regina King      |

一起來練習吧！

以資料驅動的 SQL 決策制定