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10_Wiki/Topic_Programming/Topic_SQL/SQL_Sum.md

@@ -0,0 +1,74 @@
+---
+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).