Membatasi hasil grup

Pengantar Oracle SQL

Hadrien Lacroix

Content Developer

Kembali ke contoh

SELECT Composer, AVG(Milliseconds)
FROM Track
WHERE UnitPrice = 0.99
GROUP BY Composer

| Composer        | AVG(Milliseconds) |
|-----------------|-------------------|
| Antonio Vivaldi | 199,086.0         |
| Pearl Jam       | 94,197.0          |
| Jimmy Page      | 474,888.3         |
| Carlos Santana  | 499,234.3         |
| ...             | ...               |

Bagaimana dengan memfilter setelah pengelompokan?

Batasan WHERE

WHERE tidak bisa memfilter hasil grup
- Fungsi grup tidak boleh dipakai di klausa WHERE

Contoh batasan WHERE

SELECT Composer, AVG(Milliseconds)
FROM Track
GROUP BY Composer
WHERE AVG(Milliseconds) > 200000

syntax error at or near "WHERE"
LINE 4: WHERE AVG(Milliseconds) > 200000
        ^

HAVING

SELECT Composer, AVG(Milliseconds)
FROM Track
GROUP BY Composer
HAVING AVG(Milliseconds) > 200000

| composer    | avg    |
|-------------|--------|
| George Duke | 274155 |
| Miles Davis | 391146 |
| R. Carless  | 251585 |
| ...         | ...    |

Membatasi hasil grup dengan HAVING

Alur klausa HAVING

HAVING

SELECT Composer, MAX(Milliseconds)
FROM Track
GROUP BY Composer
HAVING MAX(Milliseconds) > 200000

| composer    | max    |
|-------------|--------|
| George Duke | 274155 |
| Miles Davis | 907520 |
| R. Carless  | 251585 |
| ...         | ...    |

Contoh lain

SELECT Composer, SUM(UnitPrice)
FROM Track
WHERE GenreId = 1
GROUP BY Composer
HAVING COUNT(*) > 4

| composer      | sum  |
|---------------|------|
| AC/DC         | 7.92 |
| Chris Cornell | 9.90 |
| Eddie Vedder  | 8.91 |
| ...           | ...  |

Pedoman

Fungsi grup di SELECT dan HAVING bisa berbeda
HAVING selalu memakai fungsi grup

Urutan operasi:

Baris difilter oleh WHERE lalu dikelompokkan (GROUP BY)
Fungsi grup diterapkan ke tiap grup
Grup difilter dengan HAVING, lalu ditampilkan

Ayo berlatih!

Pengantar Oracle SQL