---
id: sql-exists
title: "SQL Exists"
category: "Database"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["SQL EXISTS Operator", "EXISTS operator", "SQL 존재 확인"]
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", "exists", "subquery"]
raw_sources: ["https://www.w3schools.com/sql/sql_exists.asp"]
applied_in: []
github_commit: ""
---

# [[SQL Exists]]

## 🎯 한 줄 통찰 (One-line insight)
EXISTS tests whether a correlated subquery returns any row at all, evaluating to TRUE the moment one match is found — a boolean existence check rather than a value comparison. [S1]

## 🧠 핵심 개념 (Core concepts)
- **EXISTS operator** — used in a WHERE clause to check whether a subquery returns any rows; TRUE if at least one row, FALSE otherwise. [S1]
- **Syntax** — `SELECT column_name(s) FROM table_name WHERE EXISTS (subquery);`. [S1]
- **Correlated subquery** — the subquery typically references the outer query's table (e.g. `Products.SupplierID = Suppliers.supplierID`) to test existence per outer row. [S1]

## 📖 세부 내용 (Details)
- Suppliers with at least one product priced under 10: [S1]
```sql
SELECT SupplierName
FROM Suppliers
WHERE EXISTS (
  SELECT ProductName
  FROM Products
  WHERE Products.SupplierID = Suppliers.supplierID AND Price < 10
);
```
- Same pattern, different threshold (Price = 22), illustrating that EXISTS only cares about row presence, not the queried column's actual values. [S1]

## ⚖️ 모순 및 업데이트 (Contradictions & updates)
소스에서 모순되는 정보는 발견되지 않음.

## 🛠️ 적용 사례 (Applied in summary)
현재 발견된 실제 적용 사례가 없습니다 — IN (SELECT ...)과 유사한 목적(서브쿼리 기반 필터링)이지만, EXISTS는 값이 아닌 행의 존재 여부만 확인한다는 차이가 있다. [S1]

## 💻 코드 패턴 (Code patterns)
Correlated EXISTS subquery (SQL):
```sql
SELECT SupplierName
FROM Suppliers
WHERE EXISTS (
  SELECT ProductName
  FROM Products
  WHERE Products.SupplierID = Suppliers.supplierID AND Price < 10
);
```

## ✅ 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 In]], [[SQL Any]], [[SQL All]]
- **참조 맥락:** 서브쿼리 결과의 "존재 여부"만 확인하면 되는 필터링에 사용 — 값 비교가 필요하면 IN/ANY/ALL을 대신 고려.

## 📚 출처 (Sources)
- [S1] W3Schools — SQL EXISTS Operator — https://www.w3schools.com/sql/sql_exists.asp

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