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<!DOCTYPE html>
<html lang="fr">
<head>
<meta charset="UTF-8">
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<title>SQL & Bases de données — Guide Interactif</title>
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<body>
<header>
<h1>SQL & Bases de données</h1>
<p>Requêtes, optimisation, transactions, modélisation</p>
</header>
<nav>
<button class="tab-btn active" onclick="showTab('overview')">Vue d'ensemble</button>
<button class="tab-btn" onclick="showTab('queries')">Requêtes SELECT</button>
<button class="tab-btn" onclick="showTab('joins')">Jointures</button>
<button class="tab-btn" onclick="showTab('index')">Index & Performance</button>
<button class="tab-btn" onclick="showTab('transactions')">Transactions ACID</button>
<button class="tab-btn" onclick="showTab('modeling')">Modélisation</button>
<button class="tab-btn" onclick="showTab('quiz')">Quiz</button>
</nav>
<!-- VUE D'ENSEMBLE -->
<section id="overview" class="active">
<h2>Vue d'ensemble</h2>
<div class="grid g2">
<div class="card">
<h4>Types de bases de données</h4>
<table>
<tr><th>Type</th><th>Modèle</th><th>Exemples</th><th>Usage</th></tr>
<tr><td><strong>Relationnel (SQL)</strong></td><td>Tables + clés</td><td>PostgreSQL, MySQL, SQLite</td><td>OLTP, données structurées</td></tr>
<tr><td><strong>Document</strong></td><td>JSON/BSON</td><td>MongoDB, CouchDB</td><td>Contenu flexible</td></tr>
<tr><td><strong>Clé-Valeur</strong></td><td>Hash map</td><td>Redis, DynamoDB</td><td>Cache, sessions</td></tr>
<tr><td><strong>Colonne</strong></td><td>Wide column</td><td>Cassandra, HBase</td><td>OLAP, time series</td></tr>
<tr><td><strong>Graphe</strong></td><td>Nœuds + arêtes</td><td>Neo4j, Amazon Neptune</td><td>Relations complexes</td></tr>
<tr><td><strong>Search</strong></td><td>Index inversé</td><td>Elasticsearch</td><td>Recherche full-text</td></tr>
</table>
</div>
<div class="card">
<h4>Architecture RDBMS</h4>
<div class="info-box">
<strong>Query Parser</strong> → vérifie la syntaxe SQL<br>
<strong>Query Optimizer</strong> → choisit le meilleur plan d'exécution<br>
<strong>Execution Engine</strong> → exécute les opérations relationnelles<br>
<strong>Buffer Pool</strong> → cache des pages disque en mémoire<br>
<strong>WAL (Write-Ahead Log)</strong> → durabilité et crash recovery<br>
<strong>Storage Engine</strong> → InnoDB (MySQL), heap/btree (PostgreSQL)
</div>
<div class="info-box blue" style="margin-top:.5rem">
<strong>OLTP vs OLAP</strong><br>
OLTP : transactions rapides, données récentes → normalisé<br>
OLAP : agrégations sur historique → dénormalisé, colonnes
</div>
</div>
</div>
<div class="grid g3" style="margin-top:1rem">
<div class="card">
<h4>Schéma d'une table</h4>
<div class="codeblk"><span class="c-kw">CREATE TABLE</span> users (
id <span class="c-val">SERIAL</span> <span class="c-kw">PRIMARY KEY</span>,
email <span class="c-val">VARCHAR</span>(255) <span class="c-kw">UNIQUE NOT NULL</span>,
name <span class="c-val">TEXT</span>,
role_id <span class="c-val">INT</span> <span class="c-kw">REFERENCES</span> roles(id)
<span class="c-kw">ON DELETE SET NULL</span>,
created <span class="c-val">TIMESTAMPTZ</span> <span class="c-kw">DEFAULT NOW</span>(),
<span class="c-kw">CONSTRAINT</span> valid_email
<span class="c-kw">CHECK</span> (email <span class="c-op">LIKE</span> <span class="c-str">'%@%'</span>)
);</div>
</div>
<div class="card">
<h4>Types de données PostgreSQL</h4>
<table>
<tr><th>Catégorie</th><th>Types</th></tr>
<tr><td>Entiers</td><td>SMALLINT, INT, BIGINT, SERIAL</td></tr>
<tr><td>Décimaux</td><td>NUMERIC(p,s), FLOAT, REAL</td></tr>
<tr><td>Texte</td><td>VARCHAR(n), TEXT, CHAR(n)</td></tr>
<tr><td>Date/Heure</td><td>DATE, TIME, TIMESTAMP, INTERVAL</td></tr>
<tr><td>Booléen</td><td>BOOLEAN (true/false/null)</td></tr>
<tr><td>JSON</td><td>JSON, JSONB (indexable)</td></tr>
<tr><td>Tableaux</td><td>INT[], TEXT[]</td></tr>
<tr><td>UUID</td><td>UUID (gen_random_uuid())</td></tr>
</table>
</div>
<div class="card">
<h4>Contraintes</h4>
<table>
<tr><th>Contrainte</th><th>Effet</th></tr>
<tr><td>PRIMARY KEY</td><td>Unicité + NOT NULL</td></tr>
<tr><td>UNIQUE</td><td>Valeur unique dans la colonne</td></tr>
<tr><td>NOT NULL</td><td>Interdit NULL</td></tr>
<tr><td>FOREIGN KEY</td><td>Intégrité référentielle</td></tr>
<tr><td>CHECK</td><td>Expression booléenne</td></tr>
<tr><td>DEFAULT</td><td>Valeur par défaut</td></tr>
<tr><td>EXCLUDE</td><td>Contrainte généralisée</td></tr>
</table>
</div>
</div>
</section>
<!-- REQUÊTES SELECT -->
<section id="queries">
<h2>Requêtes SELECT avancées</h2>
<div class="grid g2">
<div class="card">
<h4>Agrégations</h4>
<div class="codeblk"><span class="c-comment">-- Agrégations de base</span>
<span class="c-kw">SELECT</span>
department,
<span class="c-fn">COUNT</span>(*) <span class="c-kw">AS</span> total,
<span class="c-fn">AVG</span>(salary) <span class="c-kw">AS</span> avg_sal,
<span class="c-fn">MAX</span>(salary) <span class="c-kw">AS</span> max_sal,
<span class="c-fn">SUM</span>(salary) <span class="c-kw">AS</span> payroll
<span class="c-kw">FROM</span> employees
<span class="c-kw">WHERE</span> active = <span class="c-val">true</span>
<span class="c-kw">GROUP BY</span> department
<span class="c-kw">HAVING</span> <span class="c-fn">COUNT</span>(*) > <span class="c-val">5</span>
<span class="c-kw">ORDER BY</span> avg_sal <span class="c-kw">DESC</span>
<span class="c-kw">LIMIT</span> <span class="c-val">10</span>;</div>
<div class="info-box" style="margin-top:.5rem;font-size:.82rem">
<strong>Ordre d'exécution SQL :</strong> FROM → JOIN → WHERE → GROUP BY → HAVING → SELECT → DISTINCT → ORDER BY → LIMIT
</div>
</div>
<div class="card">
<h4>Window Functions</h4>
<div class="codeblk"><span class="c-comment">-- ROW_NUMBER, RANK, DENSE_RANK</span>
<span class="c-kw">SELECT</span>
name, department, salary,
<span class="c-fn">ROW_NUMBER</span>() <span class="c-kw">OVER</span> (
<span class="c-kw">PARTITION BY</span> department
<span class="c-kw">ORDER BY</span> salary <span class="c-kw">DESC</span>
) <span class="c-kw">AS</span> rank_in_dept,
<span class="c-fn">LAG</span>(salary) <span class="c-kw">OVER</span> (
<span class="c-kw">PARTITION BY</span> department
<span class="c-kw">ORDER BY</span> hire_date
) <span class="c-kw">AS</span> prev_salary,
<span class="c-fn">SUM</span>(salary) <span class="c-kw">OVER</span> (
<span class="c-kw">PARTITION BY</span> department
) <span class="c-kw">AS</span> dept_total
<span class="c-kw">FROM</span> employees;</div>
</div>
</div>
<div class="grid g2" style="margin-top:1rem">
<div class="card">
<h4>CTE (Common Table Expressions)</h4>
<div class="codeblk"><span class="c-comment">-- CTE récursif : arbre hiérarchique</span>
<span class="c-kw">WITH RECURSIVE</span> org_chart <span class="c-kw">AS</span> (
<span class="c-comment">-- Cas de base : CEO</span>
<span class="c-kw">SELECT</span> id, name, manager_id, <span class="c-val">0</span> <span class="c-kw">AS</span> depth
<span class="c-kw">FROM</span> employees
<span class="c-kw">WHERE</span> manager_id <span class="c-kw">IS NULL</span>
<span class="c-kw">UNION ALL</span>
<span class="c-comment">-- Cas récursif</span>
<span class="c-kw">SELECT</span> e.id, e.name, e.manager_id, oc.depth + <span class="c-val">1</span>
<span class="c-kw">FROM</span> employees e
<span class="c-kw">JOIN</span> org_chart oc <span class="c-kw">ON</span> e.manager_id = oc.id
)
<span class="c-kw">SELECT</span> <span class="c-fn">REPEAT</span>(<span class="c-str">' '</span>, depth) || name <span class="c-kw">AS</span> hierarchy
<span class="c-kw">FROM</span> org_chart;</div>
</div>
<div class="card">
<h4>Sous-requêtes & EXISTS</h4>
<div class="codeblk"><span class="c-comment">-- Sous-requête corrélée</span>
<span class="c-kw">SELECT</span> name, salary
<span class="c-kw">FROM</span> employees e1
<span class="c-kw">WHERE</span> salary > (
<span class="c-kw">SELECT AVG</span>(salary)
<span class="c-kw">FROM</span> employees e2
<span class="c-kw">WHERE</span> e2.department = e1.department
);
<span class="c-comment">-- EXISTS vs IN (EXISTS s'arrête au 1er match)</span>
<span class="c-kw">SELECT</span> * <span class="c-kw">FROM</span> orders o
<span class="c-kw">WHERE EXISTS</span> (
<span class="c-kw">SELECT</span> <span class="c-val">1</span> <span class="c-kw">FROM</span> order_items i
<span class="c-kw">WHERE</span> i.order_id = o.id
<span class="c-kw">AND</span> i.quantity > <span class="c-val">100</span>
);</div>
</div>
</div>
<div class="card" style="margin-top:1rem">
<h4>Fonctions de fenêtrage — référence rapide</h4>
<table>
<tr><th>Fonction</th><th>Description</th><th>Exemple d'usage</th></tr>
<tr><td>ROW_NUMBER()</td><td>Numéro unique par partition</td><td>Pagination, déduplication</td></tr>
<tr><td>RANK()</td><td>Rang avec trous</td><td>Classements</td></tr>
<tr><td>DENSE_RANK()</td><td>Rang sans trous</td><td>Top N par groupe</td></tr>
<tr><td>LAG(col, n)</td><td>Valeur de la ligne précédente</td><td>Variation jour/jour</td></tr>
<tr><td>LEAD(col, n)</td><td>Valeur de la ligne suivante</td><td>Prévisions</td></tr>
<tr><td>FIRST_VALUE(col)</td><td>1ère valeur de la fenêtre</td><td>Comparaison au premier</td></tr>
<tr><td>NTILE(n)</td><td>Découpe en n buckets</td><td>Percentiles, quartiles</td></tr>
<tr><td>PERCENT_RANK()</td><td>Rang relatif [0,1]</td><td>Distributions</td></tr>
</table>
</div>
</section>
<!-- JOINTURES -->
<section id="joins">
<h2>Jointures</h2>
<p style="color:var(--muted);margin-bottom:1rem">Cliquez sur une jointure pour voir le détail</p>
<div class="grid g3">
<div class="card clickable join-box" style="border-color:#2563eb;background:rgba(37,99,235,.05)" onclick="selectJoin('inner')">
<h4 style="color:#2563eb">INNER JOIN</h4>
<p style="font-size:.82rem">Intersection — lignes qui ont une correspondance dans les deux tables</p>
<div class="detail-panel" id="join-inner">
<div class="codeblk"><span class="c-kw">SELECT</span> u.name, o.total
<span class="c-kw">FROM</span> users u
<span class="c-kw">INNER JOIN</span> orders o
<span class="c-kw">ON</span> u.id = o.user_id;</div>
<p style="font-size:.8rem;margin-top:.4rem">Exclut les users sans commandes ET les commandes sans user.</p>
</div>
</div>
<div class="card clickable join-box" style="border-color:#7c3aed;background:rgba(124,58,237,.05)" onclick="selectJoin('left')">
<h4 style="color:#7c3aed">LEFT JOIN</h4>
<p style="font-size:.82rem">Toutes les lignes gauche + correspondances droite (NULL si absent)</p>
<div class="detail-panel" id="join-left">
<div class="codeblk"><span class="c-kw">SELECT</span> u.name, o.total
<span class="c-kw">FROM</span> users u
<span class="c-kw">LEFT JOIN</span> orders o
<span class="c-kw">ON</span> u.id = o.user_id;
<span class="c-comment">-- users sans commandes → o.total = NULL</span></div>
<p style="font-size:.8rem;margin-top:.4rem">Garder les lignes gauche sans correspondance → <code>WHERE o.id IS NULL</code></p>
</div>
</div>
<div class="card clickable join-box" style="border-color:#f59e0b;background:rgba(245,158,11,.05)" onclick="selectJoin('right')">
<h4 style="color:#f59e0b">RIGHT JOIN</h4>
<p style="font-size:.82rem">Toutes les lignes droite + correspondances gauche</p>
<div class="detail-panel" id="join-right">
<div class="codeblk"><span class="c-kw">SELECT</span> u.name, o.total
<span class="c-kw">FROM</span> users u
<span class="c-kw">RIGHT JOIN</span> orders o
<span class="c-kw">ON</span> u.id = o.user_id;
<span class="c-comment">-- Rare : préférer LEFT JOIN avec tables inversées</span></div>
</div>
</div>
<div class="card clickable join-box" style="border-color:#16a34a;background:rgba(22,163,74,.05)" onclick="selectJoin('full')">
<h4 style="color:#16a34a">FULL OUTER JOIN</h4>
<p style="font-size:.82rem">Union — toutes les lignes des deux tables</p>
<div class="detail-panel" id="join-full">
<div class="codeblk"><span class="c-kw">SELECT</span> COALESCE(u.name, <span class="c-str">'Inconnu'</span>), o.total
<span class="c-kw">FROM</span> users u
<span class="c-kw">FULL OUTER JOIN</span> orders o
<span class="c-kw">ON</span> u.id = o.user_id;</div>
<p style="font-size:.8rem;margin-top:.4rem">NULLs des deux côtés pour les non-correspondances.</p>
</div>
</div>
<div class="card clickable join-box" style="border-color:#dc2626;background:rgba(220,38,38,.05)" onclick="selectJoin('cross')">
<h4 style="color:#dc2626">CROSS JOIN</h4>
<p style="font-size:.82rem">Produit cartésien — m × n lignes</p>
<div class="detail-panel" id="join-cross">
<div class="codeblk"><span class="c-kw">SELECT</span> sizes.s, colors.c
<span class="c-kw">FROM</span> sizes <span class="c-kw">CROSS JOIN</span> colors;
<span class="c-comment">-- 5 tailles × 8 couleurs = 40 combinaisons</span></div>
<p style="font-size:.8rem;margin-top:.4rem">Attention aux grandes tables : 1000 × 1000 = 1M lignes !</p>
</div>
</div>
<div class="card clickable join-box" style="border-color:#0891b2;background:rgba(8,145,178,.05)" onclick="selectJoin('self')">
<h4 style="color:#0891b2">SELF JOIN</h4>
<p style="font-size:.82rem">Une table jointe avec elle-même</p>
<div class="detail-panel" id="join-self">
<div class="codeblk"><span class="c-kw">SELECT</span> e.name, m.name <span class="c-kw">AS</span> manager
<span class="c-kw">FROM</span> employees e
<span class="c-kw">LEFT JOIN</span> employees m
<span class="c-kw">ON</span> e.manager_id = m.id;</div>
<p style="font-size:.8rem;margin-top:.4rem">Nécessite des alias pour distinguer les deux rôles.</p>
</div>
</div>
</div>
<div class="card" style="margin-top:1rem">
<h4>Pièges des jointures</h4>
<div class="grid g3" style="margin-top:.5rem">
<div class="info-box red">
<strong>Duplication</strong><br>
JOIN sur une colonne non unique → explosion du nombre de lignes. Vérifier avec COUNT avant.
</div>
<div class="info-box">
<strong>NULL dans les conditions</strong><br>
NULL != NULL en SQL. Un INNER JOIN exclut toujours les NULLs du côté de la clé étrangère.
</div>
<div class="info-box green">
<strong>Performance</strong><br>
Filtrer avant de joindre (WHERE avant JOIN dans les sous-requêtes). Indexer les colonnes de JOIN.
</div>
</div>
</div>
</section>
<!-- INDEX & PERFORMANCE -->
<section id="index">
<h2>Index & Performance</h2>
<div class="grid g2">
<div class="card">
<h4>Types d'index PostgreSQL</h4>
<div class="grid" style="gap:.5rem;margin-top:.5rem">
<div class="card clickable" onclick="toggleDetail('idx-btree')">
<strong>B-Tree</strong> <span class="badge badge-green">Défaut</span>
<p style="font-size:.82rem;margin-top:.3rem">Égalité, inégalité, BETWEEN, ORDER BY, LIKE 'prefix%'</p>
<div class="detail-panel" id="idx-btree">
<div class="codeblk"><span class="c-kw">CREATE INDEX</span> idx_email <span class="c-kw">ON</span> users(email);
<span class="c-kw">CREATE INDEX</span> idx_comp <span class="c-kw">ON</span> orders(user_id, created_at <span class="c-kw">DESC</span>);</div>
Arbre équilibré. O(log n) pour recherche, insertion, suppression.
</div>
</div>
<div class="card clickable" onclick="toggleDetail('idx-hash')">
<strong>Hash</strong> <span class="badge badge-blue">Égalité seule</span>
<p style="font-size:.82rem;margin-top:.3rem">Plus rapide que B-Tree pour = mais inutilisable pour < ></p>
<div class="detail-panel" id="idx-hash">
<div class="codeblk"><span class="c-kw">CREATE INDEX</span> idx_token <span class="c-kw">ON</span> sessions <span class="c-kw">USING</span> hash(token);</div>
O(1) pour lookup exact. Ne supporte pas ORDER BY.
</div>
</div>
<div class="card clickable" onclick="toggleDetail('idx-gin')">
<strong>GIN</strong> <span class="badge badge-purple">Arrays/JSONB/Full-text</span>
<p style="font-size:.82rem;margin-top:.3rem">Generalized Inverted Index — valeurs composites</p>
<div class="detail-panel" id="idx-gin">
<div class="codeblk"><span class="c-kw">CREATE INDEX</span> idx_tags <span class="c-kw">ON</span> articles <span class="c-kw">USING</span> gin(tags);
<span class="c-kw">CREATE INDEX</span> idx_fts <span class="c-kw">ON</span> docs <span class="c-kw">USING</span> gin(<span class="c-fn">to_tsvector</span>(<span class="c-str">'french'</span>, body));</div>
</div>
</div>
<div class="card clickable" onclick="toggleDetail('idx-partial')">
<strong>Index partiel</strong> <span class="badge badge-yellow">Conditionnel</span>
<p style="font-size:.82rem;margin-top:.3rem">Index sur un sous-ensemble de lignes</p>
<div class="detail-panel" id="idx-partial">
<div class="codeblk"><span class="c-comment">-- Index uniquement sur les commandes non livrées</span>
<span class="c-kw">CREATE INDEX</span> idx_pending <span class="c-kw">ON</span> orders(created_at)
<span class="c-kw">WHERE</span> status != <span class="c-str">'delivered'</span>;
<span class="c-comment">-- Plus petit, plus rapide, moins de maintenance</span></div>
</div>
</div>
</div>
</div>
<div class="card">
<h4>EXPLAIN ANALYZE</h4>
<div class="codeblk"><span class="c-kw">EXPLAIN ANALYZE</span>
<span class="c-kw">SELECT</span> u.name, <span class="c-fn">COUNT</span>(o.id)
<span class="c-kw">FROM</span> users u
<span class="c-kw">LEFT JOIN</span> orders o <span class="c-kw">ON</span> o.user_id = u.id
<span class="c-kw">GROUP BY</span> u.id;</div>
<div class="codeblk" style="margin-top:.5rem"><span class="c-comment">-- Output EXPLAIN :</span>
HashAggregate (cost=<span class="c-val">245.00..255.00</span> rows=<span class="c-val">1000</span>)
-> Hash Left Join (cost=<span class="c-val">50.00..195.00</span>)
Hash Cond: (o.user_id = u.id)
-> Seq Scan on orders <span class="c-comment">(← ⚠️ manque d'index)</span>
-> Hash
-> Index Scan on users
Index Cond: (id IS NOT NULL)</div>
<div class="info-box" style="margin-top:.5rem;font-size:.82rem">
<strong>Nodes à surveiller :</strong><br>
<span style="color:var(--red)">Seq Scan</span> sur grande table → ajouter un index<br>
<span style="color:var(--orange)">Hash Join</span> → ok pour grandes tables sans index<br>
<span style="color:var(--green)">Index Scan</span> → optimal<br>
<span style="color:var(--purple)">Nested Loop</span> → bon pour petits ensembles
</div>
</div>
</div>
<div class="grid g2" style="margin-top:1rem">
<div class="card">
<h4>Optimisations courantes</h4>
<table>
<tr><th>Problème</th><th>Solution</th></tr>
<tr><td>Seq Scan sur grande table</td><td>Ajouter index sur colonne filtrée</td></tr>
<tr><td>N+1 queries</td><td>JOIN ou chargement batch</td></tr>
<tr><td>SELECT * inutile</td><td>Sélectionner uniquement les colonnes nécessaires</td></tr>
<tr><td>LIKE '%pattern%'</td><td>GIN + pg_trgm, ou Elasticsearch</td></tr>
<tr><td>Fonction sur colonne indexée</td><td>Index fonctionnel : CREATE INDEX ON f(lower(email))</td></tr>
<tr><td>Jointures lentes</td><td>Indexer les FK, VACUUM, ANALYZE</td></tr>
<tr><td>Pagination OFFSET lente</td><td>Keyset pagination (cursor-based)</td></tr>
</table>
</div>
<div class="card">
<h4>Index composites — ordre des colonnes</h4>
<div class="info-box blue">
<strong>Règle du préfixe :</strong> un index (a, b, c) sert pour les requêtes sur (a), (a, b), (a, b, c) — mais PAS (b) ou (c) seuls.
</div>
<div class="codeblk" style="margin-top:.5rem"><span class="c-comment">-- Index (user_id, created_at) utilise par :</span>
<span class="c-kw">WHERE</span> user_id = <span class="c-val">5</span> <span class="c-comment">-- ✅</span>
<span class="c-kw">WHERE</span> user_id = <span class="c-val">5</span> <span class="c-kw">AND</span> created_at > <span class="c-val">...</span> <span class="c-comment">-- ✅</span>
<span class="c-kw">WHERE</span> created_at > <span class="c-val">...</span> <span class="c-comment">-- ❌ (full scan)</span>
<span class="c-comment">-- Columne sélective en premier</span>
<span class="c-comment">-- Colonne d'égalité avant colonne de range</span></div>
</div>
</div>
</section>
<!-- TRANSACTIONS ACID -->
<section id="transactions">
<h2>Transactions ACID & Isolation</h2>
<div class="grid g2">
<div class="card">
<h4>Propriétés ACID</h4>
<div style="display:grid;gap:.5rem;margin-top:.5rem">
<div class="info-box">
<strong style="color:#2563eb">A — Atomicité</strong><br>
Tout ou rien. Si une opération échoue, ROLLBACK complet.
</div>
<div class="info-box green">
<strong style="color:#16a34a">C — Cohérence</strong><br>
La base passe d'un état valide à un autre état valide. Contraintes toujours respectées.
</div>
<div class="info-box purple">
<strong style="color:#7c3aed">I — Isolation</strong><br>
Les transactions concurrentes ne s'interfèrent pas (selon le niveau choisi).
</div>
<div class="info-box">
<strong style="color:var(--acc)">D — Durabilité</strong><br>
Après COMMIT, les données survivent aux crashes (WAL / fsync).
</div>
</div>
</div>
<div class="card">
<h4>Syntaxe des transactions</h4>
<div class="codeblk"><span class="c-kw">BEGIN</span>; <span class="c-comment">-- ou START TRANSACTION</span>
<span class="c-kw">UPDATE</span> accounts
<span class="c-kw">SET</span> balance = balance - <span class="c-val">100</span>
<span class="c-kw">WHERE</span> id = <span class="c-val">1</span>;
<span class="c-kw">UPDATE</span> accounts
<span class="c-kw">SET</span> balance = balance + <span class="c-val">100</span>
<span class="c-kw">WHERE</span> id = <span class="c-val">2</span>;
<span class="c-comment">-- Sauvegarde intermédiaire</span>
<span class="c-kw">SAVEPOINT</span> after_debit;
<span class="c-comment">-- En cas d'erreur : retour au savepoint</span>
<span class="c-kw">ROLLBACK TO</span> after_debit;
<span class="c-kw">COMMIT</span>; <span class="c-comment">-- ou ROLLBACK</span></div>
</div>
</div>
<div class="card" style="margin-top:1rem">
<h4>Niveaux d'isolation — cliquez pour détailler</h4>
<div id="iso-detail" style="display:none;background:var(--bg);border:1px solid var(--border);border-radius:.5rem;padding:1rem;margin-bottom:.5rem"></div>
<div class="iso-card" onclick="showIso('read_uncommitted')">
<div><strong>READ UNCOMMITTED</strong> <span class="badge badge-red">Dangereux</span></div>
<span class="iso-level">Niveau 0</span>
</div>
<div class="iso-card" onclick="showIso('read_committed')">
<div><strong>READ COMMITTED</strong> <span class="badge badge-yellow">Défaut PostgreSQL</span></div>
<span class="iso-level">Niveau 1</span>
</div>
<div class="iso-card" onclick="showIso('repeatable_read')">
<div><strong>REPEATABLE READ</strong> <span class="badge badge-blue">Recommandé</span></div>
<span class="iso-level">Niveau 2</span>
</div>
<div class="iso-card" onclick="showIso('serializable')">
<div><strong>SERIALIZABLE</strong> <span class="badge badge-green">Niveau maximum</span></div>
<span class="iso-level">Niveau 3</span>
</div>
<h4 style="margin-top:1rem">Anomalies de concurrence</h4>
<div class="anomaly-grid">
<div class="anomaly-cell" style="background:var(--border);font-weight:700">Niveau</div>
<div class="anomaly-cell" style="background:var(--border);font-weight:700">Dirty Read</div>
<div class="anomaly-cell" style="background:var(--border);font-weight:700">Non-Repeatable</div>
<div class="anomaly-cell" style="background:var(--border);font-weight:700">Phantom Read</div>
<div class="anomaly-cell">READ UNCOMMITTED</div>
<div class="anomaly-cell no">Possible</div>
<div class="anomaly-cell no">Possible</div>
<div class="anomaly-cell no">Possible</div>
<div class="anomaly-cell">READ COMMITTED</div>
<div class="anomaly-cell yes">Évité</div>
<div class="anomaly-cell no">Possible</div>
<div class="anomaly-cell no">Possible</div>
<div class="anomaly-cell">REPEATABLE READ</div>
<div class="anomaly-cell yes">Évité</div>
<div class="anomaly-cell yes">Évité</div>
<div class="anomaly-cell no">Possible*</div>
<div class="anomaly-cell">SERIALIZABLE</div>
<div class="anomaly-cell yes">Évité</div>
<div class="anomaly-cell yes">Évité</div>
<div class="anomaly-cell yes">Évité</div>
</div>
<p style="font-size:.78rem;color:var(--muted);margin-top:.3rem">* PostgreSQL REPEATABLE READ évite aussi les phantom reads via MVCC</p>
</div>
<div class="card" style="margin-top:1rem">
<h4>MVCC — Multi-Version Concurrency Control</h4>
<div class="grid g2">
<div class="info-box blue">
<strong>Principe :</strong> chaque transaction voit un snapshot cohérent au moment de son démarrage. Les lectures ne bloquent pas les écritures et vice-versa.
</div>
<div class="info-box">
<strong>xmin / xmax :</strong> chaque tuple garde l'ID de transaction qui l'a créé (xmin) et celle qui l'a supprimé/mis à jour (xmax). VACUUM nettoie les tuples morts.
</div>
</div>
</div>
</section>
<!-- MODÉLISATION -->
<section id="modeling">
<h2>Modélisation & Normalisation</h2>
<div class="grid g2">
<div class="card">
<h4>Formes normales</h4>
<table>
<tr><th>Forme</th><th>Règle</th></tr>
<tr><td><strong>1NF</strong></td><td>Valeurs atomiques, pas de groupes répétitifs</td></tr>
<tr><td><strong>2NF</strong></td><td>1NF + pas de dépendance partielle à la clé</td></tr>
<tr><td><strong>3NF</strong></td><td>2NF + pas de dépendance transitive</td></tr>
<tr><td><strong>BCNF</strong></td><td>3NF + tout déterminant est une super-clé</td></tr>
<tr><td><strong>4NF</strong></td><td>BCNF + pas de dépendances multi-valuées</td></tr>
<tr><td><strong>5NF</strong></td><td>4NF + pas de dépendances de jointure</td></tr>
</table>
<div class="info-box" style="margin-top:.5rem;font-size:.82rem">
En pratique : viser 3NF/BCNF pour OLTP. Dénormaliser sciemment pour les performances OLAP.
</div>
</div>
<div class="card">
<h4>Patterns de modélisation</h4>
<div class="grid" style="gap:.5rem;margin-top:.5rem">
<div class="info-box">
<strong>One-to-Many (1:N)</strong><br>
FK dans la table "many". Ex: users.id → orders.user_id
</div>
<div class="info-box blue">
<strong>Many-to-Many (N:N)</strong><br>
Table de jonction. Ex: products ↔ categories via product_categories(product_id, category_id)
</div>
<div class="info-box green">
<strong>Polymorphisme</strong><br>
Table parente + tables filles (héritage de table) OU discriminant + nullable FKs
</div>
<div class="info-box purple">
<strong>EAV (Entity-Attribute-Value)</strong><br>
Attributs dynamiques. Flexible mais difficile à interroger. Préférer JSONB.
</div>
</div>
</div>
</div>
<div class="grid g2" style="margin-top:1rem">
<div class="card">
<h4>Exemple : schéma e-commerce normalisé</h4>
<div class="codeblk"><span class="c-kw">CREATE TABLE</span> categories (
id <span class="c-val">SERIAL PRIMARY KEY</span>, name <span class="c-val">TEXT</span> <span class="c-kw">NOT NULL</span>
);
<span class="c-kw">CREATE TABLE</span> products (
id <span class="c-val">SERIAL PRIMARY KEY</span>,
name <span class="c-val">TEXT</span> <span class="c-kw">NOT NULL</span>,
price <span class="c-val">NUMERIC</span>(10,2) <span class="c-kw">NOT NULL CHECK</span> (price > 0),
cat_id <span class="c-val">INT</span> <span class="c-kw">REFERENCES</span> categories(id)
);
<span class="c-kw">CREATE TABLE</span> orders (
id <span class="c-val">SERIAL PRIMARY KEY</span>,
user_id <span class="c-val">INT</span> <span class="c-kw">REFERENCES</span> users(id),
created_at <span class="c-val">TIMESTAMPTZ DEFAULT NOW</span>(),
status <span class="c-val">TEXT</span> <span class="c-kw">CHECK</span>(status <span class="c-kw">IN</span> (<span class="c-str">'pending','paid','shipped'</span>))
);
<span class="c-kw">CREATE TABLE</span> order_items (
order_id <span class="c-val">INT</span> <span class="c-kw">REFERENCES</span> orders(id) <span class="c-kw">ON DELETE CASCADE</span>,
product_id <span class="c-val">INT</span> <span class="c-kw">REFERENCES</span> products(id),
qty <span class="c-val">INT</span> <span class="c-kw">NOT NULL CHECK</span> (qty > 0),
unit_price <span class="c-val">NUMERIC</span>(10,2) <span class="c-kw">NOT NULL</span>,
<span class="c-kw">PRIMARY KEY</span> (order_id, product_id)
);</div>
</div>
<div class="card">
<h4>Migrations & versionning</h4>
<div class="info-box blue">
<strong>Outils :</strong> Flyway, Liquibase, Alembic (Python), golang-migrate, Prisma Migrate
</div>
<div class="codeblk" style="margin-top:.5rem"><span class="c-comment">-- V1__create_users.sql</span>
<span class="c-kw">CREATE TABLE</span> users (...);
<span class="c-comment">-- V2__add_role.sql</span>
<span class="c-kw">ALTER TABLE</span> users
<span class="c-kw">ADD COLUMN</span> role <span class="c-val">TEXT DEFAULT</span> <span class="c-str">'user'</span>;</div>
<div class="info-box red" style="margin-top:.5rem;font-size:.82rem">
<strong>Règles :</strong> toujours écrire des migrations idempotentes, tester le rollback, ne jamais modifier une migration déjà appliquée en production.
</div>
</div>
</div>
</section>
<!-- QUIZ -->
<section id="quiz">
<h2>Quiz — SQL & Bases de données</h2>
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<div id="quiz-score"></div>
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read_uncommitted:{label:'READ UNCOMMITTED',desc:'Lit les données non committées des autres transactions (dirty reads). Quasi jamais utilisé.',sql:'SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;',danger:'⚠️ Peut lire des données qui seront annulées par un ROLLBACK.'},
read_committed:{label:'READ COMMITTED',desc:'Lit uniquement les données committées. Chaque SELECT dans la transaction voit un snapshot différent.',sql:'SET TRANSACTION ISOLATION LEVEL READ COMMITTED;',danger:'⚠️ Non-repeatable reads : deux SELECT dans la même transaction peuvent retourner des données différentes.'},
repeatable_read:{label:'REPEATABLE READ',desc:'Garantit que le même SELECT retourne les mêmes lignes. PostgreSQL MVCC évite aussi les phantom reads.',sql:'SET TRANSACTION ISOLATION LEVEL REPEATABLE READ;',danger:'ℹ️ En PostgreSQL, serialization failure possible → retry nécessaire.'},
serializable:{label:'SERIALIZABLE',desc:'Niveau le plus fort. Les transactions s\'exécutent comme si elles étaient séquentielles. PostgreSQL utilise SSI (Serializable Snapshot Isolation).',sql:'SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;',danger:'ℹ️ Coût de performance plus élevé. Retry obligatoire en cas de conflit.'}
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{q:"Quel est l'ordre d'exécution correct des clauses SQL ?",opts:["SELECT → FROM → WHERE → GROUP BY → HAVING","FROM → WHERE → GROUP BY → HAVING → SELECT → ORDER BY","WHERE → FROM → SELECT → GROUP BY → HAVING","FROM → SELECT → WHERE → HAVING → GROUP BY"],a:1},
{q:"Quelle jointure retourne TOUTES les lignes de la table gauche, même sans correspondance ?",opts:["INNER JOIN","RIGHT JOIN","LEFT JOIN","CROSS JOIN"],a:2},
{q:"Quel type d'index PostgreSQL est optimal pour les recherches dans des tableaux ou du JSONB ?",opts:["B-Tree","Hash","GIN","BRIN"],a:2},
{q:"Que signifie le 'I' dans ACID ?",opts:["Intégrité","Isolation","Idempotence","Initialisation"],a:1},
{q:"Quelle anomalie consiste à lire des données modifiées par une transaction non encore committée ?",opts:["Phantom read","Non-repeatable read","Dirty read","Lost update"],a:2},
{q:"Quel niveau d'isolation est le défaut dans PostgreSQL ?",opts:["READ UNCOMMITTED","REPEATABLE READ","SERIALIZABLE","READ COMMITTED"],a:3},
{q:"La fenêtre PARTITION BY dans une window function...",opts:["Filtre les résultats comme WHERE","Divise les résultats en groupes pour le calcul de fenêtrage","Crée des partitions de table physiques","Trie les résultats"],a:1},
{q:"Qu'est-ce que MVCC ?",opts:["Multi-Value Column Control","Multi-Version Concurrency Control","Master-Value Cache Control","Modèle Vectoriel de Cohérence Conditionnelle"],a:1},
{q:"Pour paginer efficacement sur de grandes tables, quelle approche est recommandée ?",opts:["OFFSET/LIMIT classique","Keyset pagination (cursor-based)","FETCH FIRST N ROWS","TOP N"],a:1},
{q:"Qu'est-ce qu'une CTE récursive ?",opts:["Une requête qui s'exécute plusieurs fois","Une expression de table commune qui se référence elle-même","Un index récursif","Un trigger auto-référentiel"],a:1},
{q:"Quelle forme normale interdit les dépendances transitives ?",opts:["1NF","2NF","3NF","BCNF"],a:2},
{q:"Que fait EXPLAIN ANALYZE en PostgreSQL ?",opts:["Génère un plan théorique","Exécute réellement la requête et retourne le plan + métriques","Optimise automatiquement la requête","Affiche les index utilisables"],a:1}
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