April 2025
Beginner to intermediate
570 pages
12h 7m
Italian
Content preview from SQL Cookbook, 2a edizione
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Capitolo 12. Reporting e rimodellamento
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Questo capitolo presenta delle query che potrebbero esserti utili per creare dei report. In genere si tratta di considerazioni di formattazione specifiche per i report e di diversi livelli di aggregazione. Un altro punto focale di questo capitolo è la trasposizione o il pivoting dei risultati: rimodellare i dati trasformando le righe in colonne.
In generale, queste ricette hanno in comune il fatto che ti permettono di presentare i dati in formati o forme diverse da quelle in cui sono memorizzati. Man mano che il tuo livello di confidenza con il pivoting aumenterà, troverai senza dubbio altri usi oltre a quelli presentati in questo capitolo.
12.1 Fare perno su un insieme di risultati in un'unica riga
Problema
Vuoi prendere i valori da gruppi di righe e trasformarli in colonne in una singola riga per gruppo. Ad esempio, hai un set di risultati che mostra il numero di dipendenti in ogni reparto:
DEPTNO CNT
------ ----------
10 3
20 5
30 6
Vorresti riformattare l'output in modo che l'insieme dei risultati abbia il seguente aspetto:
DEPTNO_10 DEPTNO_20 DEPTNO_30
--------- ---------- ----------
3 5 6
Questo è un classico esempio di dati presentati in una forma diversa da quella in cui sono memorizzati.
Soluzione
Trasponi l'insieme dei risultati usando CASE e la funzione aggregata SUM:
1 select sum(case ...
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