Crearea grupurilor de date
Introducere în Oracle SQL
Hadrien Lacroix
Content Developer
Gruparea datelor
Informații de grup
| 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 |
| ... | ... |
Care este durata medie a pieselor scrise de fiecare compozitor?
GROUP BY- împarte rândurile unui tabel în grupuri
- utilizează funcții de grup pentru a obține informații rezumative pentru fiecare grup
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 și 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 și 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 și 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 și 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 |
| ... | ... |
Reguli
Orice coloană sau expresie din instrucțiunea SELECT care nu este o funcție agregat trebuie inclusă în clauza 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
Reguli
Orice coloană sau expresie din lista SELECT care nu este o funcție agregat trebuie inclusă în clauza 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 |
| ... | ... | ... |
Reguli
Expresiile specificate în GROUP BY nu trebuie incluse obligatoriu în instrucțiunea SELECT
SELECT AVG(Milliseconds)
FROM Track
GROUP BY Composer
| AVG(Milliseconds) |
|-------------------|
| 199,086.0 |
| 94,197.0 |
| 474,888.3 |
| 499,234.3 |
| ... |
Coloane multiple
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 |
| ... | ... | ... |
Să exersăm!
Introducere în Oracle SQL
