2nd/10_Wiki/Dev/Topic_SQL/SQL_Where.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-where	SQL Where	Database	draft	conceptual		SQL WHERE Clause WHERE clause SQL 조건절		B	0.9	2026-07-04	2026-07-04			sql database w3schools where filter operators	https://www.w3schools.com/sql/sql_where.asp

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]

SELECT * FROM Customers
WHERE Country = 'Mexico';

• Numeric fields are not quoted: [S1]

SELECT * FROM Customers
WHERE CustomerID = 1;

• Operators other than = can filter the search, e.g. greater-than: [S1]

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):

SELECT * FROM Customers
WHERE Country = 'Mexico';

Filter by numeric comparison (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).