Créer des groupes de données
Introduction à Oracle SQL
Hadrien Lacroix
Content Developer
Regrouper des données
Informations par groupe
| Composer | Milliseconds |
|-----------------|--------------|
| Antonio Vivaldi | 199,086 |
| Pearl Jam | 122,801 |
| Pearl Jam | 65,593 |
| Jimmy Page | 401,920 |
| Jimmy Page | 386,063 |
| Jimmy Page | 132,702 |
| Jimmy Page | 189,675 |
| Jimmy Page | 126,641 |
| Carlos Santana | 318,432 |
| Carlos Santana | 296,437 |
| Carlos Santana | 882,834 |
| ... | ... |
Quelle est la durée moyenne des morceaux par compositeur ?
GROUP BY- divise les lignes d'une table en groupes
- utilisez des fonctions d'agrégation pour résumer chaque groupe
GROUP BY
SELECT Composer, AVG(Milliseconds)
FROM Track
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 |
| ... | ... |
GROUP BY et WHERE
SELECT Composer, AVG(Milliseconds)
FROM Track
WHERE Genre = 1
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 |
| ... | ... |
GROUP BY et ORDER BY
SELECT Composer, AVG(Milliseconds) AS Average
FROM Track
GROUP BY Composer
ORDER BY AVG(Milliseconds)
| Composer | AVG(Milliseconds) |
|-----------------|-------------------|
| Pearl Jam | 94,197.0 |
| Antonio Vivaldi | 199,086.0 |
| Jimmy Page | 474,888.3 |
| Carlos Santana | 499,234.3 |
| ... | ... |
GROUP BY et ORDER BY
SELECT Composer, AVG(Milliseconds) AS Average
FROM Track
GROUP BY Composer
ORDER BY 2
| Composer | AVG(Milliseconds) |
|-----------------|-------------------|
| Pearl Jam | 94,197.0 |
| Antonio Vivaldi | 199,086.0 |
| Jimmy Page | 474,888.3 |
| Carlos Santana | 499,234.3 |
| ... | ... |
GROUP BY et ORDER BY
SELECT Composer, AVG(Milliseconds) AS Average
FROM Track
GROUP BY Composer
ORDER BY Average
| Composer | Average |
|-----------------|-------------------|
| Pearl Jam | 94,197.0 |
| Antonio Vivaldi | 199,086.0 |
| Jimmy Page | 474,888.3 |
| Carlos Santana | 499,234.3 |
| ... | ... |
Directives
Toute colonne ou expression dans l'instruction SELECT qui n'est pas une fonction d'agrégation doit figurer dans la clause GROUP BY.
SELECT Composer, AVG(Milliseconds), UnitPrice
FROM Track
GROUP BY Composer
column "track.unitprice" must appear in the GROUP BY clause or be used in an aggregate function
LINE 2: SELECT Composer, AVG(Milliseconds), UnitPrice
Directives
Toute colonne ou expression dans la liste SELECT qui n'est pas une fonction d'agrégation doit figurer dans la clause GROUP BY.
SELECT Composer, AVG(Milliseconds), MAX(UnitPrice)
FROM Track
GROUP BY Composer
| Composer | AVG(Milliseconds) | MAX(UnitPrice) |
|-----------------|-------------------|----------------|
| Antonio Vivaldi | 199,086.0 | 0.99 |
| Pearl Jam | 94,197.0 | 0.99 |
| Jimmy Page | 474,888.3 | 0.99 |
| Carlos Santana | 499,234.3 | 0.99 |
| ... | ... | ... |
Directives
Les expressions indiquées dans GROUP BY n'ont pas besoin d'être incluses dans l'instruction SELECT.
SELECT AVG(Milliseconds)
FROM Track
GROUP BY Composer
| AVG(Milliseconds) |
|-------------------|
| 199,086.0 |
| 94,197.0 |
| 474,888.3 |
| 499,234.3 |
| ... |
Colonnes multiples
SELECT Country, City, COUNT(CustomerId)
FROM Customer
GROUP BY Country, City
| Country | City | COUNT(CustomerId) |
|-----------|---------------------|-------------------|
| Argentina | Buenos Aires | 1 |
| Australia | Sidney | 1 |
| Austria | Vienne | 1 |
| Belgium | Brussels | 1 |
| Brazil | Brasilia | 1 |
| Brazil | São José dos Campos | 1 |
| Brazil | São Paulo | 2 |
| ... | ... | ... |
Passons à la pratique !
Introduction à Oracle SQL
