Agregacje – podsumowywanie danych

Podejmowanie decyzji na podstawie danych w SQL

Bart Baesens

Professor Data Science and Analytics

Przegląd agregacji

SELECT AVG(renting_price)
FROM movies;

SELECT AVG(renting_price)
FROM movies;

Wybrane funkcje agregujące w SQL

SELECT COUNT(*)
FROM actors;

SELECT COUNT(name)
FROM actors;

SELECT COUNT(year_of_birth)
FROM actors;

SELECT DISTINCT country
FROM customers;

| country       |
|---------------|
| Spain         | 
| Great Britain | 
| Austria       | 
| Poland        | 
| ............. |

SELECT COUNT(DISTINCT country)
FROM customers;

SELECT DISTINCT rating
FROM renting
ORDER BY rating;

| rating |
|--------|
| 1      | 
| ...... | 
| 10     | 
| null   |

SELECT AVG(renting_price) AS average_price, 
         COUNT(DISTINCT genre) AS number_genres
FROM movies;

| average_price | number_genres |
|---------------|---------------|
| 2.21          | 8             |

Podejmowanie decyzji na podstawie danych w SQL