November 2024
Intermediate to advanced
974 pages
28h 12m
French
Content preview from Manuel de cuisine MySQL, 4e éditionBecome an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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Chapitre 16. Utilisation des jointures et des sous-requêtes
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16.0 Introduction
La plupart des requêtes des chapitres précédents utilisaient une seule table, mais pour toute applicationd'une complexité même modérée, tu auras probablement besoin d'utiliser plusieurs tables. Il est impossible de répondre à certaines questions à l'aide d'une seule table, et la véritable puissance d'une base de données relationnelle entre en jeu lorsque tu combines les informations provenant de plusieurs sources :
Combine les lignes des tableaux pour obtenir des informations plus complètes que celles que l'on peut obtenir à partir des tableaux individuels.
Maintiens les résultats intermédiaires pour une opération en plusieurs étapes.
Modifie les lignes d'un tableau en fonction des informations d'un autre tableau.
Ce chapitre se concentre sur deux types d'instructions qui utilisent plusieurs tables : les jointures entre les tables et les sous-requêtes qui imbriquent une SELECT dans une autre. Il aborde les sujets suivants :
- Comparer des tableaux pour trouver des correspondances ou des non-concordances
Pour résoudre ces problèmes, tu dois savoir quels types de jointures s'appliquent. Les jointures internes montrent quelles lignes d'une table correspondent à des lignes d'une autre table. Les jointures externes montrent les lignes correspondantes mais trouvent également les lignes d'une ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.