Geneste query

Data-driven beslissingen nemen met SQL

Irene Ortner

Data Scientist at Applied Statistics

Geneste query

SELECT-blok in WHERE- of HAVING-clausules
Binnenste query geeft één of meerdere waarden terug
Gebruik de uitkomst van de binnenste query om rijen in een andere query te selecteren

De binnenste query

Stap 1: De binnenste query

SELECT DISTINCT customer_id
FROM renting
WHERE rating <= 3

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

Resultaat in de WHERE-clausule

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

De buitenste query

Stap 2: De buitenste query

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

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

Geneste query in de HAVING-clausule

Stap 1: De binnenste query

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

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

Geneste query in de HAVING-clausule

Stap 2: De buitenste query

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 |

Wie spelen er in de film Ray?

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      |

Laten we oefenen!

Data-driven beslissingen nemen met SQL