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Antigravity Agent e9cbf23ab5 docs(10_Wiki): Dev 폴더 누락분 반영 — Topic_Programming으로 통합

이전 재구성 작업에서 Dev/ 폴더가 누락되었던 것을 반영.

- Dev/Topic_Programming(중첩 폴더, 78개)은 Dev 자체 최상위 폴더들
  (Architecture/Conventions/Engineering_Intelligence 등)과 완전 중복이라 제거.
- Dev 최상위 엔지니어링 지식 폴더(Architecture/Conventions/Engineering_Intelligence/
  Failure_Library/Generalized_Principles/Language/Pattern_Catalog/Platform_Guides/
  Subsystems, 77개)는 이미 Topic_Programming/Topic_Programming에 더 최신 버전이
  존재해 중복 제거(고유 콘텐츠 1개는 예외 처리하여 이동 보존).
- Dev의 W3Schools 언어 튜토리얼 폴더(Topic_C/CPP/CSS/CSharp/HOWTO/HTML/Java/
  JavaScript/PHP/Python/SQL/W3CSS, 1201개)는 전부 Topic_Programming 하위로 이동.
- 에이전트 운영 상태(.astra/docs)는 그대로 유지, 콘텐츠 폴더만 정리.
- Topic_Programming 최종 문서 수: 2784 → 3985.

2026-07-05 00:39:13 +09:00

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title

SQL Self Join

🎯 한 줄 통찰 (One-line insight)

A self join is a regular join where a table is joined with itself, made possible by giving the same table two different aliases so rows can be compared against other rows in the same table. [S1]

🧠 핵심 개념 (Core concepts)

Self join — a regular join where the table is joined with itself. [S1]
Syntax — SELECT column_name(s) FROM table1 T1, table1 T2 WHERE condition; where T1 and T2 are different aliases for the same table. [S1]

🧩 추출된 패턴 (Extracted patterns)

Exclude self-match — a self join typically needs a condition like A.CustomerID <> B.CustomerID to avoid matching each row with itself. [S1]
Dual-alias comparison — the same table appears twice with different aliases (A, B) purely so SQL can treat the two references as independent row sets for comparison. [S1]

📖 세부 내용 (Details)

Match customers that share the same city (excluding matching a customer with itself): [S1]

SELECT A.CustomerName AS CustomerName1, B.CustomerName AS CustomerName2, A.City
FROM Customers A, Customers B
WHERE A.CustomerID <> B.CustomerID
AND A.City = B.City
ORDER BY A.City;

⚖️ 모순 및 업데이트 (Contradictions & updates)

소스에서 모순되는 정보는 발견되지 않음.

🛠️ 적용 사례 (Applied in summary)

현재 발견된 실제 적용 사례가 없습니다 — 조직도(상사-부하 관계), 동일 도시 고객 찾기 등 "같은 테이블 내 행 간 관계"를 표현할 때 쓰이는 전형적 패턴이다. [S1]

💻 코드 패턴 (Code patterns)

Self join with alias and self-match exclusion (SQL):

SELECT A.CustomerName AS CustomerName1, B.CustomerName AS CustomerName2, A.City
FROM Customers A, Customers B
WHERE A.CustomerID <> B.CustomerID
AND A.City = B.City
ORDER BY A.City;

✅ 검증 상태 및 신뢰도

상태: draft
검증 단계: conceptual
출처 신뢰도: B (W3Schools — widely used educational reference, not a primary standards body)
신뢰 점수: 0.88
중복 검사 결과: 신규 생성 (New discovery)

🔗 지식 그래프 (Knowledge Graph)

상위/루트: SQL Tutorial
관련 개념: SQL Joins, SQL Aliases, SQL Inner Join
참조 맥락: 같은 테이블 내 행 간 관계를 표현해야 할 때(계층 구조, 동일 그룹 찾기) 재사용.

📚 출처 (Sources)

[S1] W3Schools — SQL Self Join — https://www.w3schools.com/sql/sql_join_self.asp

📝 변경 이력 (Change history)

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

3.1 KiB Raw Blame History