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10_Wiki/Topic_Programming/Topic_SQL/SQL_Primary_Key.md

@@ -0,0 +1,73 @@
+---
+id: sql-primary-key
+title: "SQL Primary Key"
+category: "Database"
+status: "draft"
+verification_status: "conceptual"
+canonical_id: ""
+aliases: ["SQL PRIMARY KEY Constraint", "PRIMARY KEY constraint"]
+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", "primarykey", "constraints"]
+raw_sources: ["https://www.w3schools.com/sql/sql_primarykey.asp"]
+applied_in: []
+github_commit: ""
+---
+
+# [[SQL Primary Key]]
+
+## 🎯 한 줄 통찰 (One-line insight)
+PRIMARY KEY uniquely identifies every row (as a UNIQUE + NOT NULL combination), can span multiple columns, and is the anchor that FOREIGN KEY constraints in other tables point to. [S1]
+
+## 🧠 핵심 개념 (Core concepts)
+- **PRIMARY KEY constraint** — uniquely identifies each record; ensures unique values and cannot contain NULL (combination of UNIQUE + NOT NULL). [S1]
+- **One per table** — a table can have only ONE PRIMARY KEY, which can be a single column or a combination of columns (composite key). [S1]
+- **FK anchor** — the primary key is the target that FOREIGN KEY constraints in other tables reference, enforcing referential integrity. [S1]
+- **ALTER TABLE prerequisite** — adding a PRIMARY KEY via ALTER TABLE requires the column(s) already be declared NOT NULL. [S1]
+
+## 📖 세부 내용 (Details)
+- Single-column PK on creation: `CREATE TABLE Persons (ID int PRIMARY KEY, LastName varchar(255) NOT NULL, FirstName varchar(255), Age int);`. [S1]
+- Composite (multi-column) PK: `PRIMARY KEY (ID, LastName)`, or named: `CONSTRAINT PK_Person PRIMARY KEY (ID, LastName)`. [S1]
+- Add PK to existing table: `ALTER TABLE Persons ADD PRIMARY KEY (ID);`. [S1]
+- Drop PK: `ALTER TABLE Persons DROP CONSTRAINT PK_Person;` (SQL Server/Oracle/Access) vs. `ALTER TABLE Persons DROP PRIMARY KEY;` (MySQL). [S1]
+
+## ⚖️ 모순 및 업데이트 (Contradictions & updates)
+- **드롭 문법 차이**: SQL Server/Oracle/Access는 `DROP CONSTRAINT`, MySQL은 `DROP PRIMARY KEY`를 사용. [S1]
+
+## 🛠️ 적용 사례 (Applied in summary)
+현재 발견된 실제 적용 사례가 없습니다 — FOREIGN KEY 챕터에서 이 PRIMARY KEY를 참조하는 관계가 바로 이어서 다뤄진다. [S1]
+
+## 💻 코드 패턴 (Code patterns)
+Composite primary key (SQL):
+```sql
+CREATE TABLE Persons (
+    ID int,
+    LastName varchar(255),
+    FirstName varchar(255),
+    Age int,
+    CONSTRAINT PK_Person PRIMARY KEY (ID, LastName)
+);
+```
+
+## ✅ 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 Foreign Key]], [[SQL Not Null]], [[SQL Unique]], [[SQL Auto Increment]]
+- **참조 맥락:** 테이블 설계의 핵심 — FOREIGN KEY가 참조하는 대상이자, 대개 AUTO INCREMENT와 함께 쓰인다.
+
+## 📚 출처 (Sources)
+- [S1] W3Schools — SQL PRIMARY KEY Constraint — https://www.w3schools.com/sql/sql_primarykey.asp
+
+## 📝 변경 이력 (Change history)
+- 2026-07-04: Initial draft synthesized from the W3Schools "SQL PRIMARY KEY Constraint" page (Astra wiki-curation, P-Reinforce v3.1 format).