---
id: sql-sum
title: "SQL Sum"
category: "Database"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["SQL SUM() Function", "SUM function", "SQL 합계"]
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", "sum", "aggregate"]
raw_sources: ["https://www.w3schools.com/sql/sql_sum.asp"]
applied_in: []
github_commit: ""
---

# [[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):
```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).