April 2025
Beginner to intermediate
570 pages
12h 7m
Italian
Content preview from SQL Cookbook, 2a edizione
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Capitolo 10. Lavorare con gli intervalli
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Questo capitolo tratta delle query "quotidiane" che coinvolgono gli intervalli. Gli intervalli sono comuni nella vita di tutti i giorni. Ad esempio, i progetti su cui lavoriamo coprono periodi di tempo consecutivi. In SQL è spesso necessario cercare intervalli, generare intervalli o manipolare in altro modo dati basati su intervalli. Le query che leggerai qui sono un po' più complesse rispetto a quelle dei capitoli precedenti, ma sono altrettanto comuni e inizieranno a darti un'idea di ciò che SQL può davvero fare per te quando impari a sfruttarlo appieno.
10.1 Individuare un intervallo di valori consecutivi
Problema
Vuoi determinare quali righe rappresentano un intervallo di progetti consecutivi. Considera il seguente set di risultati della vista V, che contiene i dati di un progetto e le sue date di inizio e fine:
select *
from V
PROJ_ID PROJ_START PROJ_END
------- ----------- -----------
1 01-JAN-2020 02-JAN-2020
2 02-JAN-2020 03-JAN-2020
3 03-JAN-2020 04-JAN-2020
4 04-JAN-2020 05-JAN-2020
5 06-JAN-2020 07-JAN-2020
6 16-JAN-2020 17-JAN-2020
7 17-JAN-2020 18-JAN-2020
8 18-JAN-2020 19-JAN-2020
9 19-JAN-2020 20-JAN-2020
10 21-JAN-2020 22-JAN-2020
11 26-JAN-2020 27-JAN-2020
12 27-JAN-2020 28-JAN-2020
13 28-JAN-2020 29-JAN-2020
14 29-JAN-2020 30-JAN-2020
Escludendo la prima riga, il PROJ_START di ogni ...
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