---
id: sql-where
title: "SQL Where"
category: "Database"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["SQL WHERE Clause", "WHERE clause", "SQL 조건절"]
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", "where", "filter", "operators"]
raw_sources: ["https://www.w3schools.com/sql/sql_where.asp"]
applied_in: []
github_commit: ""
---

# [[SQL Where]]

## 🎯 한 줄 통찰 (One-line insight)
The WHERE clause filters records to only those that fulfill a specific condition, and works not just in SELECT but also in UPDATE and DELETE statements. [S1]

## 🧠 핵심 개념 (Core concepts)
- **WHERE clause** — extracts only records that satisfy a given condition; usable in `SELECT`, `UPDATE`, `DELETE`. [S1]
- **WHERE syntax** — `SELECT column1, column2, ... FROM table_name WHERE condition;`. [S1]
- **Text vs. numeric fields** — text values must be wrapped in single quotes (`'Mexico'`), while numeric fields should NOT be quoted. [S1]
- **Comparison operators in WHERE** — `=`, `>`, `<`, `>=`, `<=`, `<>` (or `!=` in some SQL dialects), plus `BETWEEN`, `LIKE`, `IN`. [S1]

## 🧩 추출된 패턴 (Extracted patterns)
- **Quote-by-type rule** — quote text values, never quote numeric values, when writing WHERE conditions. [S1]
- **WHERE is statement-agnostic** — the same filtering syntax generalizes across SELECT/UPDATE/DELETE rather than being SELECT-specific. [S1]

## ⚖️ 비교 및 선택 기준 (Comparison & decision criteria)

| 항목 (Option) | 장점 | 단점 | 언제 선택 |
|---|---|---|---|
| **`=` 단일 값 비교** | 가장 단순하고 명확함 | 범위·패턴 조건 표현 불가 | 정확히 일치하는 값 하나를 찾을 때 |
| **`BETWEEN` / `IN` / `LIKE`** | 범위·목록·패턴 조건을 간결하게 표현 | 단순 비교보다 읽기/성능 비용이 더 들 수 있음 | 범위 필터, 다중 후보값, 부분 문자열 매칭이 필요할 때 |

## 📖 세부 내용 (Details)
- Select all customers from Mexico: [S1]
```sql
SELECT * FROM Customers
WHERE Country = 'Mexico';
```
- Numeric fields are not quoted: [S1]
```sql
SELECT * FROM Customers
WHERE CustomerID = 1;
```
- Operators other than `=` can filter the search, e.g. greater-than: [S1]
```sql
SELECT * FROM Customers
WHERE CustomerID > 80;
```
- Operators available in the WHERE clause: `=` (equal), `>` (greater than), `<` (less than), `>=` (greater than or equal), `<=` (less than or equal), `<>` (not equal — written `!=` in some SQL versions), `BETWEEN` (range), `LIKE` (pattern search), `IN` (multiple possible values). [S1]

## ⚖️ 모순 및 업데이트 (Contradictions & updates)
- **`<>` vs `!=`**: 소스 자체가 "일부 SQL 버전에서는 `<>`가 `!=`로 쓰일 수 있다"고 명시 — 표준 표기(`<>`)와 방언별 표기(`!=`)가 공존함을 알려줌. [S1]

## 🛠️ 적용 사례 (Applied in summary)
현재 발견된 실제 적용 사례가 없습니다 — WHERE 절은 이후 AND/OR/NOT, JOIN, GROUP BY 등 조건부 쿼리 전반에서 반복적으로 재사용되는 핵심 문법이다. [S1]

## 💻 코드 패턴 (Code patterns)
Filter by text value (SQL):
```sql
SELECT * FROM Customers
WHERE Country = 'Mexico';
```
Filter by numeric comparison (SQL):
```sql
SELECT * FROM Customers
WHERE CustomerID > 80;
```

## ✅ 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 Select]], [[SQL And]], [[SQL Like]], [[SQL Between]], [[SQL In]]
- **참조 맥락:** 조건부 데이터 필터링의 기반 문서 — AND/OR/NOT, LIKE, BETWEEN, IN 챕터가 모두 이 WHERE 절 문법을 확장한다.

## 📚 출처 (Sources)
- [S1] W3Schools — SQL WHERE Clause — https://www.w3schools.com/sql/sql_where.asp

## 📝 변경 이력 (Change history)
- 2026-07-04: Initial draft synthesized from the W3Schools "SQL WHERE Clause" page (Astra wiki-curation, P-Reinforce v3.1 format).
