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10_Wiki/Dev/Topic_PHP/PHP_MySQL_Select.md

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+---
+id: php-mysql-select
+title: "PHP MySQL Select"
+category: "Programming_Language"
+status: "draft"
+verification_status: "conceptual"
+canonical_id: ""
+aliases: ["fetch_assoc", "num_rows", "PHP MySQL 데이터 조회"]
+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", "select"]
+raw_sources: ["https://www.w3schools.com/php/php_mysql_select.asp"]
+applied_in: []
+github_commit: ""
+---
+
+# [[PHP MySQL Select]]
+
+## 🎯 한 줄 통찰 (One-line insight)
+Retrieving results requires checking the row count BEFORE looping — `$result->num_rows > 0` gates the `while` loop, since calling `fetch_assoc()` on a zero-row result set just returns false immediately, making the explicit "0 results" branch necessary for clear user feedback rather than a silently empty output. [S1]
+
+## 🧠 핵심 개념 (Core concepts)
+- **`SELECT column1, column2 FROM table`** — selects specific columns; `SELECT *` selects all columns. [S1]
+- **`$conn->query($sql)`** — executes and returns a result object/set. [S1]
+- **`$result->num_rows`** (MySQLi OOP) / **`mysqli_num_rows($result)`** (procedural) — row count check before looping. [S1]
+- **`$result->fetch_assoc()`** (MySQLi OOP) / **`mysqli_fetch_assoc($result)`** (procedural) — pulls one row as an associative array per call; used inside a `while` loop. [S1]
+- **PDO equivalents** — `$result->rowCount()` for row count, `$result->fetch()` for one row at a time. [S1]
+
+## 📖 세부 내용 (Details)
+- MySQLi OOP select+loop: `$sql = "SELECT id, firstname, lastname FROM MyGuests"; $result = $conn->query($sql); if ($result->num_rows > 0) { while($row = $result->fetch_assoc()) { echo "id: " . $row["id"]. " - Name: " . $row["firstname"]. " " . $row["lastname"]. "<br>"; } } else { echo "0 results"; }`. [S1]
+- MySQLi procedural equivalent: `$result = mysqli_query($conn, $sql); if (mysqli_num_rows($result) > 0) { while($row = mysqli_fetch_assoc($result)) {...} }`. [S1]
+- PDO equivalent: `$result = $conn->query($sql); if ($result->rowCount() > 0) { while($row = $result->fetch()) {...} } else { echo "No records found."; }`. [S1]
+
+## ⚖️ 모순 및 업데이트 (Contradictions & updates)
+소스에서 모순되는 정보는 발견되지 않음.
+
+## 🛠️ 적용 사례 (Applied in summary)
+현재 발견된 실제 적용 사례가 없습니다 — id/firstname/lastname을 HTML 테이블로 렌더링하는 것이 조회 결과 출력의 표준 패턴이다. [S1]
+
+## 💻 코드 패턴 (Code patterns)
+Selecting and looping through results, checking row count first (PHP/MySQLi):
+```php
+$sql = "SELECT id, firstname, lastname FROM MyGuests";
+$result = $conn->query($sql);
+if ($result->num_rows > 0) {
+    while ($row = $result->fetch_assoc()) {
+        echo "id: " . $row["id"] . " - Name: " . $row["firstname"] . " " . $row["lastname"] . "<br>";
+    }
+} else {
+    echo "0 results";
+}
+```
+
+## ✅ 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 Prepared Statements]], [[PHP MySQL Select Where]]
+- **참조 맥락:** 데이터 조회 기초 — WHERE 조건 필터링(Select Where) 챕터로 이어짐.
+
+## 📚 출처 (Sources)
+- [S1] W3Schools — PHP MySQL Select Data — https://www.w3schools.com/php/php_mysql_select.asp
+
+## 📝 변경 이력 (Change history)
+- 2026-07-04: Initial draft synthesized from the W3Schools "PHP MySQL Select Data" page (Astra wiki-curation, P-Reinforce v3.1 format).