April 2025
Beginner to intermediate
570 pages
12h 7m
Italian
Content preview from SQL Cookbook, 2a edizione
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Capitolo 4. Inserire, aggiornare e cancellare
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I capitoli precedenti si sono concentrati sulle tecniche di query di base, tutte incentrate sul compito di estrarre i dati da un database. Questo capitolo cambia le carte in tavola e si concentra sulle tre aree tematiche seguenti:
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Inserire nuovi record nel database
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Aggiornare i record esistenti
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Eliminare i record che non si desiderano più
Per facilitare la ricerca quando ne hai bisogno, le ricette di questo capitolo sono state raggruppate per argomento: tutte le ricette di inserimento vengono prima, seguite da quelle di aggiornamento e infine da quelle di cancellazione dei dati.
L'inserimento è di solito un'attività semplice. Inizia con il semplice problema di inserire una singola riga. Molte volte, però, è più efficiente utilizzare un approccio basato sugli insiemi per creare nuove righe. A tal fine, troverai anche delle tecniche per inserire molte righe alla volta.
Allo stesso modo, l'aggiornamento e la cancellazione iniziano come operazioni semplici. Puoi aggiornare un record e cancellare un record. Ma puoi anche aggiornare interi gruppi di record in una sola volta e in modi molto potenti. E ci sono molti modi pratici per eliminare i record. Ad esempio, puoi eliminare le righe di una tabella a seconda che esistano o meno in un'altra tabella.
SQL ha anche un modo, un'aggiunta relativamente ...
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