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title

SQL Sum

🎯 한 줄 통찰 (One-line insight)

SUM() totals a numeric column, ignores NULLs, and can take an expression (not just a bare column) — including a value computed by joining in another table's price. [S1]

🧠 핵심 개념 (Core concepts)

SUM() function — calculates the total sum of values within a numeric column; ignores NULL values. [S1]
Syntax — SELECT SUM(column_name) FROM table_name WHERE condition;. [S1]
SUM() with an expression — the argument can be an expression like Quantity * 10, not just a column reference. [S1]
SUM() with GROUP BY — returns a sum per group. [S1]

🧩 추출된 패턴 (Extracted patterns)

Join-then-sum for real totals — instead of assuming a flat unit price, joining the detail table to the actual Products table and summing Price * Quantity gives the real total, illustrating that SUM() arguments can encode business logic via JOIN + expression. [S1]

📖 세부 내용 (Details)

Basic sum: SELECT SUM(Quantity) FROM OrderDetails;. [S1]
With WHERE: SELECT SUM(Quantity) FROM OrderDetails WHERE ProductId = 11;. [S1]
With alias: SELECT SUM(Quantity) AS total FROM OrderDetails;. [S1]
With GROUP BY: SELECT OrderID, SUM(Quantity) AS [Total Quantity] FROM OrderDetails GROUP BY OrderID;. [S1]
With an expression: SELECT SUM(Quantity * 10) FROM OrderDetails;. [S1]
With a JOIN for real prices: SELECT SUM(Price * Quantity) FROM OrderDetails LEFT JOIN Products ON OrderDetails.ProductID = Products.ProductID;. [S1]

⚖️ 모순 및 업데이트 (Contradictions & updates)

소스에서 모순되는 정보는 발견되지 않음.

🛠️ 적용 사례 (Applied in summary)

현재 발견된 실제 적용 사례가 없습니다 — 매출/수량 합계 리포트의 기본 함수로, JOIN과 결합한 실제 매출 계산 예시가 소스에 직접 등장한다. [S1]

💻 코드 패턴 (Code patterns)

SUM with expression and JOIN (SQL):

SELECT SUM(Price * Quantity)
FROM OrderDetails
LEFT JOIN Products ON OrderDetails.ProductID = Products.ProductID;

✅ 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 Aggregate Functions, SQL Group By, SQL Left Join
참조 맥락: 합계 리포트의 기본 함수 — 표현식·JOIN과 결합해 실제 매출/수량 계산에 쓰인다.

📚 출처 (Sources)

[S1] W3Schools — SQL SUM() Function — https://www.w3schools.com/sql/sql_sum.asp

📝 변경 이력 (Change history)

2026-07-04: Initial draft synthesized from the W3Schools "SQL SUM() Function" page (Astra wiki-curation, P-Reinforce v3.1 format).

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