---
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).