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+---
+id: sql-joins
+title: "SQL Joins"
+category: "Database"
+status: "draft"
+verification_status: "conceptual"
+canonical_id: ""
+aliases: ["SQL JOIN Clause", "SQL 조인"]
+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", "join"]
+raw_sources: ["https://www.w3schools.com/sql/sql_join.asp"]
+applied_in: []
+github_commit: ""
+---
+
+# [[SQL Joins]]
+
+## 🎯 한 줄 통찰 (One-line insight)
+JOIN combines rows from two or more tables based on a related column between them, with four variants (INNER/LEFT/RIGHT/FULL) differing in which unmatched rows they keep. [S1]
+
+## 🧠 핵심 개념 (Core concepts)
+- **JOIN clause** — combines rows from two or more tables based on a related column. [S1]
+- **(INNER) JOIN** — returns only rows with matching values in both tables. [S1]
+- **LEFT (OUTER) JOIN** — returns all rows from the left table, plus matched rows from the right table. [S1]
+- **RIGHT (OUTER) JOIN** — returns all rows from the right table, plus matched rows from the left table. [S1]
+- **FULL (OUTER) JOIN** — returns all rows when there is a match in either table. [S1]
+
+## 🧩 추출된 패턴 (Extracted patterns)
+- **Related-column identification** — before writing a JOIN, identify the shared column between two tables (e.g. `CustomerID` appears in both "Orders" and "Customers"). [S1]
+
+## 📖 세부 내용 (Details)
+- Example relationship: the "Orders" table's `CustomerID` refers to the "Customers" table's `CustomerID`. [S1]
+- INNER JOIN combining the two: `SELECT Orders.OrderID, Customers.CustomerName, Orders.OrderDate FROM Orders INNER JOIN Customers ON Orders.CustomerID=Customers.CustomerID;`. [S1]
+- The four JOIN types are summarized as covering: matches-only (INNER), left-preserving (LEFT), right-preserving (RIGHT), and both-preserving (FULL). [S1]
+
+## ⚖️ 모순 및 업데이트 (Contradictions & updates)
+소스에서 모순되는 정보는 발견되지 않음.
+
+## 🛠️ 적용 사례 (Applied in summary)
+현재 발견된 실제 적용 사례가 없습니다 — 이 문서는 개론이며, 각 JOIN 유형은 이어지는 개별 챕터(Inner/Left/Right/Full/Self Join)에서 상세히 다뤄진다. [S1]
+
+## 💻 코드 패턴 (Code patterns)
+Basic INNER JOIN (SQL):
+```sql
+SELECT Orders.OrderID, Customers.CustomerName, Orders.OrderDate
+FROM Orders
+INNER JOIN Customers ON Orders.CustomerID=Customers.CustomerID;
+```
+
+## ✅ 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 Inner Join]], [[SQL Left Join]], [[SQL Right Join]], [[SQL Full Join]], [[SQL Aliases]]
+- **참조 맥락:** JOIN 계열 챕터 전체의 개론 — 이후 4가지 JOIN 유형이 각각 별도 문서로 심화된다.
+
+## 📚 출처 (Sources)
+- [S1] W3Schools — SQL Joins — https://www.w3schools.com/sql/sql_join.asp
+
+## 📝 변경 이력 (Change history)
+- 2026-07-04: Initial draft synthesized from the W3Schools "SQL Joins" page (Astra wiki-curation, P-Reinforce v3.1 format).