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.
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+---
+id: sql-self-join
+title: "SQL Self Join"
+category: "Database"
+status: "draft"
+verification_status: "conceptual"
+canonical_id: ""
+aliases: ["Self Join", "SQL 자기 조인"]
+duplicate_of: ""
+source_trust_level: "B"
+confidence_score: 0.88
+created_at: 2026-07-04
+updated_at: 2026-07-04
+review_reason: ""
+merge_history: []
+tags: ["sql", "database", "w3schools", "join", "self-join"]
+raw_sources: ["https://www.w3schools.com/sql/sql_join_self.asp"]
+applied_in: []
+github_commit: ""
+---
+
+# [[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]
+```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;
+```
+
+## ⚖️ 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):
+```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).