---
id: sql-alter-table
title: "SQL Alter Table"
category: "Database"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["SQL ALTER TABLE Statement", "ALTER TABLE", "SQL 테이블 수정"]
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", "altertable"]
raw_sources: ["https://www.w3schools.com/sql/sql_alter.asp"]
applied_in: []
github_commit: ""
---

# [[SQL Alter Table]]

## 🎯 한 줄 통찰 (One-line insight)
ALTER TABLE covers six common structural operations — add/drop/rename/modify a column, add a constraint, rename the table — with syntax that fragments by vendor for renaming and modifying columns. [S1]

## 🧠 핵심 개념 (Core concepts)
- **ALTER TABLE statement** — adds, deletes, or modifies columns in an existing table, and adds/drops constraints. [S1]
- **Common operations** — Add column, Drop column, Rename column, Modify column, Add constraint, Rename table. [S1]
- **Add column** — `ALTER TABLE table_name ADD column_name datatype;`. [S1]
- **Drop column** — `ALTER TABLE table_name DROP COLUMN column_name;` (not allowed on some database systems). [S1]
- **Rename column** — `ALTER TABLE table_name RENAME COLUMN old_name to new_name;` (SQL Server instead uses `EXEC sp_rename`). [S1]
- **Modify column** — `ALTER COLUMN ...` (SQL Server/MS Access) vs. `MODIFY ...` (MySQL/Oracle). [S1]
- **Add constraint** — `ALTER TABLE table_name ADD CONSTRAINT constraint_name constraint_definition;`. [S1]
- **Rename table** — `ALTER TABLE table_name RENAME TO new_table_name;`. [S1]

## 🧩 추출된 패턴 (Extracted patterns)
- **Vendor fragmentation on rename/modify** — renaming a column and modifying a column's type both require different syntax on SQL Server vs. MySQL/Oracle — the two operations most likely to trip up cross-database code. [S1]

## 📖 세부 내용 (Details)
- Add a column: `ALTER TABLE Customers ADD Email varchar(255);`. [S1]
- Modify a column with a new constraint (MySQL/Oracle): `ALTER TABLE Customers MODIFY Email varchar(100) NOT NULL;`. [S1]
- Add a named CHECK constraint: `ALTER TABLE Members ADD CONSTRAINT CHK_Age CHECK (Age >= 18);`. [S1]
- Rename a table: `ALTER TABLE Customers RENAME TO Clients;`. [S1]

## ⚖️ 모순 및 업데이트 (Contradictions & updates)
- **동일 의도, 다른 문법**: 컬럼 이름 변경/타입 변경이 SQL Server(`sp_rename`/`ALTER COLUMN`)와 MySQL/Oracle(`MODIFY`)에서 서로 다른 키워드를 요구함이 소스에서 명시적으로 대비됨. [S1]

## 🛠️ 적용 사례 (Applied in summary)
현재 발견된 실제 적용 사례가 없습니다 — 이미 생성된 테이블의 스키마를 점진적으로 진화시킬 때(마이그레이션) 쓰이는 핵심 문법이다. [S1]

## 💻 코드 패턴 (Code patterns)
Add a column then a constraint (SQL):
```sql
ALTER TABLE Customers
ADD Email varchar(255);

ALTER TABLE Members
ADD CONSTRAINT CHK_Age CHECK (Age >= 18);
```

## ✅ 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 Create Table]], [[SQL Constraints]], [[SQL Not Null]], [[SQL Check]]
- **참조 맥락:** 스키마 마이그레이션(컬럼/제약조건 추가·수정)의 기본 문법 — 벤더별 문법 차이를 항상 확인해야 한다.

## 📚 출처 (Sources)
- [S1] W3Schools — SQL ALTER TABLE Statement — https://www.w3schools.com/sql/sql_alter.asp

## 📝 변경 이력 (Change history)
- 2026-07-04: Initial draft synthesized from the W3Schools "SQL ALTER TABLE Statement" page (Astra wiki-curation, P-Reinforce v3.1 format).