2nd/10_Wiki/Topics/Domain_Programming/Topic_SQL/SQL_Case.md

id, title, category, status, verification_status, canonical_id, aliases, duplicate_of, source_trust_level, confidence_score, created_at, updated_at, review_reason, merge_history, tags, raw_sources, applied_in, github_commit

id	title	category	status	verification_status	canonical_id	aliases	duplicate_of	source_trust_level	confidence_score	created_at	updated_at	review_reason	merge_history	tags	raw_sources	applied_in	github_commit
sql-case	SQL Case	Database	draft	conceptual		SQL CASE Expression CASE expression SQL 조건식		B	0.9	2026-07-04	2026-07-04			sql database w3schools case conditional	https://www.w3schools.com/sql/sql_case.asp

SQL Case

🎯 한 줄 통찰 (One-line insight)

CASE works like an if-then-else chain inside a query — it stops at the first true condition, falls back to ELSE, and returns NULL if nothing matches and there's no ELSE. [S1]

🧠 핵심 개념 (Core concepts)

• CASE expression — defines different results based on specified conditions within an SQL statement. [S1]
• Short-circuit evaluation — stops at the first true condition and returns its result, like an if-then-else statement. [S1]
• ELSE fallback — if no condition is true, returns the ELSE value; without ELSE and no match, returns NULL. [S1]
• Syntax — CASE WHEN condition1 THEN result1 WHEN condition2 THEN result2 ... ELSE default_result END;. [S1]

📖 세부 내용 (Details)

• Categorize products by price into a new derived column: [S1]

SELECT ProductName, Price,
CASE
    WHEN Price < 20 THEN 'Low Cost'
    WHEN Price BETWEEN 20 AND 50 THEN 'Medium Cost'
    ELSE 'High Cost'
END AS PriceCategory
FROM Products;

⚖️ 모순 및 업데이트 (Contradictions & updates)

소스에서 모순되는 정보는 발견되지 않음.

🛠️ 적용 사례 (Applied in summary)

현재 발견된 실제 적용 사례가 없습니다 — 가격 구간처럼 값을 범주화하는 파생 컬럼을 만들 때 전형적으로 쓰인다. [S1]

💻 코드 패턴 (Code patterns)

CASE for value categorization (SQL):

SELECT ProductName, Price,
CASE
    WHEN Price < 20 THEN 'Low Cost'
    WHEN Price BETWEEN 20 AND 50 THEN 'Medium Cost'
    ELSE 'High Cost'
END AS PriceCategory
FROM Products;

✅ 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 Between, SQL Aliases, SQL Null Functions
• 참조 맥락: 값 기반 분기/범주화 파생 컬럼이 필요한 모든 쿼리의 기본 조건식.

📚 출처 (Sources)

• [S1] W3Schools — SQL CASE Expression — https://www.w3schools.com/sql/sql_case.asp

📝 변경 이력 (Change history)

• 2026-07-04: Initial draft synthesized from the W3Schools "SQL CASE Expression" page (Astra wiki-curation, P-Reinforce v3.1 format).