---
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).
