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84 lines
4.4 KiB
Markdown
84 lines
4.4 KiB
Markdown
---
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id: sql-aliases
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title: "SQL Aliases"
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category: "Database"
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status: "draft"
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verification_status: "conceptual"
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canonical_id: ""
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aliases: ["SQL Alias", "AS keyword", "SQL 별칭"]
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duplicate_of: ""
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source_trust_level: "B"
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confidence_score: 0.9
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created_at: 2026-07-04
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updated_at: 2026-07-04
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review_reason: ""
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merge_history: []
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tags: ["sql", "database", "w3schools", "alias", "join"]
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raw_sources: ["https://www.w3schools.com/sql/sql_alias.asp"]
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applied_in: []
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github_commit: ""
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---
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# [[SQL Aliases]]
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## 🎯 한 줄 통찰 (One-line insight)
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An alias, created with AS, gives a column or table a temporary, more readable name that exists only for the duration of the query — and becomes essential once tables are joined. [S1]
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## 🧠 핵심 개념 (Core concepts)
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- **Alias** — created with the `AS` keyword; makes a column name more readable; only exists for the duration of that query. [S1]
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- **Column alias syntax** — `SELECT column_name AS alias_name FROM table_name;`. [S1]
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- **Table alias syntax** — `SELECT column_name(s) FROM table_name AS alias_name;`. [S1]
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- **Aliases with spaces** — wrap in square brackets `[My Great Products]` or double quotes `"My Great Products"` (support varies by DB system). [S1]
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- **Concatenation alias** — combining multiple columns into one output column needs an alias to name the combined result. [S1]
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## 🧩 추출된 패턴 (Extracted patterns)
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- **Table alias for joins** — short aliases like `c` for customers and `o` for orders make multi-table JOIN queries shorter and more readable: `FROM customers AS c JOIN orders AS o ON c.customerID = o.customerID`. [S1]
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- **Vendor-specific concatenation syntax** — the same "combine 4 address columns into one" intent needs different syntax per DB: `+` (SQL Server), `CONCAT()` (MySQL), `||` (Oracle). [S1]
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- **When aliases matter most** — the source lists: multiple tables in a query, functions used in the query, long/unclear column names, and combined columns. [S1]
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## 📖 세부 내용 (Details)
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- Basic column alias: `SELECT CustomerID AS ID, CustomerName AS Customer FROM Customers;`. [S1]
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- Alias with spaces (bracket form): `SELECT ProductName AS [My Great Products] FROM Products;`. [S1]
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- Alias with spaces (quote form): `SELECT ProductName AS "My Great Products" FROM Products;`. [S1]
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- Concatenated column alias (SQL Server): `SELECT CustomerName, Address + ', ' + PostalCode + ' ' + City + ', ' + Country AS Address FROM Customers;`. [S1]
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- Same intent in MySQL: `SELECT CustomerName, CONCAT(Address,', ',PostalCode,', ',City,', ',Country) AS Address FROM Customers;`. [S1]
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- Same intent in Oracle: `SELECT CustomerName, (Address || ', ' || PostalCode || ' ' || City || ', ' || Country) AS Address FROM Customers;`. [S1]
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- Table alias: `SELECT * FROM Customers AS Persons;` and, for joins, `FROM customers AS c JOIN orders AS o ON c.customerID = o.customerID`. [S1]
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## ⚖️ 모순 및 업데이트 (Contradictions & updates)
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- **문자열 연결 문법이 DB마다 다름**: 동일한 "4개 컬럼 합치기" 요구가 SQL Server(`+`), MySQL(`CONCAT()`), Oracle(`||`)에서 각각 다른 연산자로 구현됨 — 표준 SQL이 아닌 방언별 차이. [S1]
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## 🛠️ 적용 사례 (Applied in summary)
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현재 발견된 실제 적용 사례가 없습니다 — 이후 JOIN 챕터 전체에서 테이블 별칭(c, o 등)이 관용적으로 재사용된다. [S1]
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## 💻 코드 패턴 (Code patterns)
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Column alias (SQL):
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```sql
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SELECT CustomerID AS ID, CustomerName AS Customer
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FROM Customers;
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```
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Table alias for a join (SQL):
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```sql
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SELECT c.CustomerName, o.OrderID
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FROM customers AS c
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JOIN orders AS o ON c.customerID = o.customerID;
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```
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## ✅ 검증 상태 및 신뢰도
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- **상태:** draft
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- **검증 단계:** conceptual
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- **출처 신뢰도:** B (W3Schools — widely used educational reference, not a primary standards body)
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- **신뢰 점수:** 0.90
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- **중복 검사 결과:** 신규 생성 (New discovery)
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## 🔗 지식 그래프 (Knowledge Graph)
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- **상위/루트:** [[SQL Tutorial]]
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- **관련 개념:** [[SQL Select]], [[SQL Joins]], [[SQL Inner Join]]
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- **참조 맥락:** 다중 테이블 JOIN 쿼리를 읽기 쉽게 만드는 표준 관용구 — 이후 모든 JOIN 챕터의 전제 지식.
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## 📚 출처 (Sources)
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- [S1] W3Schools — SQL Aliases — https://www.w3schools.com/sql/sql_alias.asp
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## 📝 변경 이력 (Change history)
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- 2026-07-04: Initial draft synthesized from the W3Schools "SQL Aliases" page (Astra wiki-curation, P-Reinforce v3.1 format).
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