Kueri dengan EXISTS

Pengambilan Keputusan Berbasis Data dengan SQL

Irene Ortner

Data Scientist at Applied Statistics

EXISTS

Kasus khusus kueri bertingkat berkorelasi.
Untuk memeriksa apakah hasil kueri berkorelasi kosong.
Mengembalikan: TRUE atau FALSE
TRUE = tidak kosong -> baris kueri luar dipilih.
FALSE = kosong
Kolom di SELECT tidak diperhitungkan - gunakan SELECT *

Film dengan setidaknya satu rating

SELECT *
FROM movies AS m
WHERE EXISTS
    (SELECT *
     FROM renting AS r
     WHERE rating IS NOT NULL 
     AND r.movie_id = m.movie_id);

Film dengan setidaknya satu rating

SELECT *
FROM renting AS r
WHERE rating IS NOT NULL 
AND r.movie_id = 11;

| renting_id | customer_id | movie_id | rating | renting_price |
|------- ----|-------------|----------|--------|---------------|

Film dengan setidaknya satu rating

SELECT *
FROM renting AS r
WHERE rating IS NOT NULL 
AND r.movie_id = 1;

| renting_id | customer_id | movie_id | rating | renting_price |
|------------|-------------|----------|--------|---------------|
| 71         | 111         | 1        | 5      | 2018-07-21    |
| 170        | 36          | 1        | 10     | 2018-10-18    |

Kueri EXISTS dengan hasil

SELECT *
FROM movies AS m
WHERE EXISTS
    (SELECT *
     FROM renting AS r
     WHERE rating IS NOT NULL 
     AND 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          |

NOT EXISTS

TRUE = tabel kosong -> baris kueri luar dipilih.

SELECT *
FROM movies AS m
WHERE NOT EXISTS
    (SELECT *
     FROM renting AS r
     WHERE rating IS NOT NULL 
     AND r.movie_id = m.movie_id);

| movie_id | title    | genre  | runtime | year_of_release | renting_price |
|----------|----------|--------|---------|-----------------|---------------|
| 11       | Showtime | Comedy | 95      | 2002            | 1.79          |

Ayo berlatih!

Pengambilan Keputusan Berbasis Data dengan SQL