2nd/10_Wiki/Dev/Topic_SQL/SQL_Alter_Table.md

id, title, category, status, verification_status, canonical_id, aliases, duplicate_of, source_trust_level, confidence_score, created_at, updated_at, review_reason, merge_history, tags, raw_sources, applied_in, github_commit

id	title	category	status	verification_status	canonical_id	aliases	duplicate_of	source_trust_level	confidence_score	created_at	updated_at	review_reason	merge_history	tags	raw_sources	applied_in	github_commit
sql-alter-table	SQL Alter Table	Database	draft	conceptual		SQL ALTER TABLE Statement ALTER TABLE SQL 테이블 수정		B	0.88	2026-07-04	2026-07-04			sql database w3schools altertable	https://www.w3schools.com/sql/sql_alter.asp

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):

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).