docs(10_Wiki): 위키 구조 정리 — 언어 튜토리얼 카테고리 폴더 제거 + 신규 자산 동기화

Topic_CSS/Topic_HTML/Topic_JavaScript/Topic_Prompt/Topic_Comfyui 등 기존 카테고리 폴더를 정리하고, Topic_Graphic/Dev 등 신규 산출물과 Topics 내부 세션/메모리 기록을 동기화.
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+---
+id: sql-count
+title: "SQL Count"
+category: "Database"
+status: "draft"
+verification_status: "conceptual"
+canonical_id: ""
+aliases: ["SQL COUNT() Function", "COUNT function", "SQL 개수 세기"]
+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: ["sql", "database", "w3schools", "count", "aggregate"]
+raw_sources: ["https://www.w3schools.com/sql/sql_count.asp"]
+applied_in: []
+github_commit: ""
+---
+
+# [[SQL Count]]
+
+## 🎯 한 줄 통찰 (One-line insight)
+COUNT() behaves differently depending on its argument — `COUNT(*)` counts all rows including NULLs, `COUNT(column)` counts non-null values, and `COUNT(DISTINCT column)` counts unique non-null values. [S1]
+
+## 🧠 핵심 개념 (Core concepts)
+- **COUNT() function** — returns the number of rows matching a specified criterion. [S1]
+- **Syntax** — `SELECT COUNT([DISTINCT] column_name | *) FROM table_name WHERE condition;`. [S1]
+- **`COUNT(*)`** — counts the total number of rows, including NULL values. [S1]
+- **`COUNT(column_name)`** — counts only non-null values in that column. [S1]
+- **`COUNT(DISTINCT column_name)`** — counts only unique, non-null values. [S1]
+
+## 🧩 추출된 패턴 (Extracted patterns)
+- **Argument choice changes semantics** — the three COUNT variants answer three different questions (total rows / filled-in rows / unique values), so picking the right one matters for correctness, not just style. [S1]
+
+## 📖 세부 내용 (Details)
+- Total row count: `SELECT COUNT(*) FROM Products;`. [S1]
+- Non-null count for a column: `SELECT COUNT(ProductName) FROM Products;`. [S1]
+- Unique non-null count: `SELECT COUNT(DISTINCT Price) FROM Products;`. [S1]
+- With WHERE: `SELECT COUNT(ProductID) FROM Products WHERE Price > 20;`. [S1]
+- With alias: `SELECT COUNT(*) AS [Number of records] FROM Products;`. [S1]
+- With GROUP BY: `SELECT COUNT(*) AS [Number of records], CategoryID FROM Products GROUP BY CategoryID;`. [S1]
+
+## ⚖️ 모순 및 업데이트 (Contradictions & updates)
+소스에서 모순되는 정보는 발견되지 않음.
+
+## 🛠️ 적용 사례 (Applied in summary)
+현재 발견된 실제 적용 사례가 없습니다 — SELECT DISTINCT 챕터에서 이미 소개된 `COUNT(DISTINCT ...)` 패턴이 여기서 정식으로 다뤄진다. [S1]
+
+## 💻 코드 패턴 (Code patterns)
+Three COUNT variants (SQL):
+```sql
+SELECT COUNT(*) FROM Products;                 -- all rows, incl. NULLs
+SELECT COUNT(ProductName) FROM Products;       -- non-null values only
+SELECT COUNT(DISTINCT Price) FROM Products;    -- unique non-null values
+```
+
+## ✅ 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:** [[SQL Tutorial]]
+- **관련 개념:** [[SQL Aggregate Functions]], [[SQL Select Distinct]], [[SQL Group By]]
+- **참조 맥락:** 행 개수를 세는 모든 리포트의 기본 함수 — DISTINCT와 결합해 고유값 개수도 셀 수 있다.
+
+## 📚 출처 (Sources)
+- [S1] W3Schools — SQL COUNT() Function — https://www.w3schools.com/sql/sql_count.asp
+
+## 📝 변경 이력 (Change history)
+- 2026-07-04: Initial draft synthesized from the W3Schools "SQL COUNT() Function" page (Astra wiki-curation, P-Reinforce v3.1 format).