docs(10_Wiki): Dev 폴더 누락분 반영 — Topic_Programming으로 통합

이전 재구성 작업에서 Dev/ 폴더가 누락되었던 것을 반영. - Dev/Topic_Programming(중첩 폴더, 78개)은 Dev 자체 최상위 폴더들 (Architecture/Conventions/Engineering_Intelligence 등)과 완전 중복이라 제거. - Dev 최상위 엔지니어링 지식 폴더(Architecture/Conventions/Engineering_Intelligence/ Failure_Library/Generalized_Principles/Language/Pattern_Catalog/Platform_Guides/ Subsystems, 77개)는 이미 Topic_Programming/Topic_Programming에 더 최신 버전이 존재해 중복 제거(고유 콘텐츠 1개는 예외 처리하여 이동 보존). - Dev의 W3Schools 언어 튜토리얼 폴더(Topic_C/CPP/CSS/CSharp/HOWTO/HTML/Java/ JavaScript/PHP/Python/SQL/W3CSS, 1201개)는 전부 Topic_Programming 하위로 이동. - 에이전트 운영 상태(.astra/docs)는 그대로 유지, 콘텐츠 폴더만 정리. - Topic_Programming 최종 문서 수: 2784 → 3985.
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+---
+id: php-mysql-connect
+title: "PHP MySQL Connect"
+category: "Programming_Language"
+status: "draft"
+verification_status: "conceptual"
+canonical_id: ""
+aliases: ["MySQLi vs PDO", "PHP MySQL 연결"]
+duplicate_of: ""
+source_trust_level: "B"
+confidence_score: 0.9
+created_at: 2026-07-04
+updated_at: 2026-07-04
+review_reason: ""
+merge_history: []
+tags: ["php", "programming", "w3schools", "mysql", "mysqli", "pdo"]
+raw_sources: ["https://www.w3schools.com/php/php_mysql_connect.asp"]
+applied_in: []
+github_commit: ""
+---
+
+# [[PHP MySQL Connect]]
+
+## 🎯 한 줄 통찰 (One-line insight)
+Switching database systems later is trivial with PDO (change the connection string + a few queries) but requires rewriting EVERYTHING with MySQLi (queries included) — since PDO works across 12 different database systems while MySQLi only works with MySQL, the choice between them is really a bet on whether the project will ever need to migrate databases. [S1]
+
+## 🧠 핵심 개념 (Core concepts)
+- **MySQLi (MySQL Improved)** — works only with MySQL; offers both object-oriented AND procedural APIs. [S1]
+- **PDO (PHP Data Objects)** — works across 12 different database systems; object-oriented only. [S1]
+- **Both support Prepared Statements** — critical for protecting against SQL injection. [S1]
+- **Connection requires 4 pieces** — server name, username, password, database name. [S1]
+- **PDO's exception-based error handling** — `PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION` — throws exceptions on query problems, caught via `catch(PDOException $e)`. [S1]
+- **Closing connections** — automatic at script end; can be forced early via `$conn->close()` (MySQLi OOP), `mysqli_close($conn)` (procedural), or `$conn = null;` (PDO). [S1]
+
+## 📖 세부 내용 (Details)
+- MySQLi OOP connection: `$conn = new mysqli($servername, $username, $password, $dbname); if ($conn->connect_error) { die("Connection failed: " . $conn->connect_error); }`. [S1]
+- MySQLi procedural connection: `$conn = mysqli_connect($servername, $username, $password, $dbname); if (!$conn) { die("Connection failed: " . mysqli_connect_error()); }`. [S1]
+- PDO connection: `try { $conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password); $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); } catch(PDOException $e) { echo "Connection failed: " . $e->getMessage(); }`. [S1]
+
+## ⚖️ 모순 및 업데이트 (Contradictions & updates)
+- **DB 전환 용이성의 차이**: PDO는 다른 DB로 전환 시 연결 문자열과 일부 쿼리만 수정하면 되지만, MySQLi는 쿼리를 포함한 전체 코드를 다시 작성해야 한다는 점이 명확히 대비됨. [S1]
+
+## 🛠️ 적용 사례 (Applied in summary)
+현재 발견된 실제 적용 사례가 없습니다 — PDO의 예외 기반 에러 처리(ERRMODE_EXCEPTION)가 데이터베이스 연결 문제를 안전하게 다루는 표준 패턴이다. [S1]
+
+## 💻 코드 패턴 (Code patterns)
+PDO connection with exception-based error handling (PHP):
+```php
+try {
+    $conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
+    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
+    echo "Connected successfully";
+} catch (PDOException $e) {
+    echo "Connection failed: " . $e->getMessage();
+}
+```
+
+## ✅ 검증 상태 및 신뢰도
+- **상태:** draft
+- **검증 단계:** conceptual
+- **출처 신뢰도:** B (W3Schools — widely used educational reference, not a primary standards body)
+- **신뢰 점수:** 0.90
+- **중복 검사 결과:** 신규 생성 (New discovery)
+
+## 🔗 지식 그래프 (Knowledge Graph)
+- **상위/루트:** [[PHP Tutorial]]
+- **관련 개념:** [[PHP MySQL Intro]], [[PHP MySQL Create DB]], [[PHP Exception]]
+- **참조 맥락:** MySQLi/PDO 연결 방식 — 데이터베이스 생성(Create DB) 챕터로 이어짐.
+
+## 📚 출처 (Sources)
+- [S1] W3Schools — PHP Connect to MySQL — https://www.w3schools.com/php/php_mysql_connect.asp
+
+## 📝 변경 이력 (Change history)
+- 2026-07-04: Initial draft synthesized from the W3Schools "PHP Connect to MySQL" page (Astra wiki-curation, P-Reinforce v3.1 format).