April 2025
Intermediate to advanced
356 pages
5h 20m
Italian
Content preview from SQL Pocket Guide, 4a edizione
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Capitolo 8. Concetti avanzati di query
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Questo capitolo tratta alcuni modi avanzati di gestire i dati con le query SQL, oltre alle sei clausole principali trattate nel Capitolo 4, "Nozioni di base sulle query", e alle parole chiave comuni trattate nel Capitolo 7, "Operatori e funzioni".
LaTabella 8-1 contiene descrizioni ed esempi di codice dei quattro concetti trattati in questo capitolo.
| Concetto | Descrizione | Esempio di codice |
|---|---|---|
Se una condizione è soddisfatta, restituisce un determinato valore. Altrimenti, restituisce un altro valore. |
SELECT house_id, CASE WHEN flg = 1 THEN 'for sale' ELSE 'sold' END FROM houses; |
|
Dividere i dati in gruppi, aggregare i dati all'interno di ogni gruppo e restituire un valore per ogni gruppo. |
SELECT zip, AVG(ft) FROM houses GROUP BY zip; |
|
Dividere i dati in gruppi, aggregare o ordinare i dati all'interno di ogni gruppo e restituire un valore per ogni riga. |
SELECT zip, ROW_NUMBER() OVER (PARTITION BY zip ORDER BY price) FROM houses; |
|
Trasforma i valori di una colonna in più colonne o consolida più colonne in un'unica colonna. Supportato da Oracle e SQL Server. |
-- Oracle syntax
SELECT *
FROM listing_info
PIVOT
(COUNT(*) FOR
room IN ('bd','br'));
|
Questo capitolo descrive ...
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