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Antigravity Agent e9cbf23ab5 docs(10_Wiki): Dev 폴더 누락분 반영 — Topic_Programming으로 통합

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2026-07-05 00:39:13 +09:00

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title

SQL Group By

🎯 한 줄 통찰 (One-line insight)

GROUP BY collapses rows sharing the same value into summary rows, and is almost always paired with an aggregate function like COUNT/SUM/AVG to compute a value per group. [S1]

🧠 핵심 개념 (Core concepts)

GROUP BY statement — groups rows with the same values into summary rows, e.g. "find the number of customers in each country". [S1]
Pairs with aggregate functions — COUNT(), MAX(), MIN(), SUM(), AVG() compute a single value per group. [S1]
Syntax — SELECT column1, aggregate_function(column2), column3, ... FROM table_name WHERE condition GROUP BY column1, column3 ORDER BY column_name;. [S1]
GROUP BY with JOIN — grouping works across joined tables, e.g. counting orders per shipper after a LEFT JOIN. [S1]

🧩 추출된 패턴 (Extracted patterns)

Group-then-sort-by-aggregate — combining GROUP BY with ORDER BY COUNT(...) DESC ranks groups by their aggregate value, a very common "top categories" reporting pattern. [S1]

📖 세부 내용 (Details)

Count customers per country: SELECT Country, COUNT(CustomerID) AS [Number of Customers] FROM Customers GROUP BY Country;. [S1]
Same, sorted by count descending: ... GROUP BY Country ORDER BY COUNT(CustomerID) DESC;. [S1]
GROUP BY with a JOIN: SELECT Shippers.ShipperName, COUNT(Orders.OrderID) AS NumberOfOrders FROM Orders LEFT JOIN Shippers ON Orders.ShipperID = Shippers.ShipperID GROUP BY ShipperName;. [S1]

⚖️ 모순 및 업데이트 (Contradictions & updates)

소스에서 모순되는 정보는 발견되지 않음.

🛠️ 적용 사례 (Applied in summary)

현재 발견된 실제 적용 사례가 없습니다 — 다음 챕터인 HAVING이 GROUP BY 결과 자체를 필터링하는 방법을 확장한다. [S1]

💻 코드 패턴 (Code patterns)

Count rows per group, sorted by count (SQL):

SELECT Country, COUNT(CustomerID) AS [Number of Customers]
FROM Customers
GROUP BY Country
ORDER BY COUNT(CustomerID) DESC;

✅ 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 Having, SQL Aggregate Functions, SQL Count, SQL Order By
참조 맥락: 집계 리포트(카테고리별 집계, 랭킹) 작성의 핵심 문법 — HAVING과 함께 이해해야 완전해진다.

📚 출처 (Sources)

[S1] W3Schools — SQL GROUP BY Statement — https://www.w3schools.com/sql/sql_groupby.asp

📝 변경 이력 (Change history)

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

3.4 KiB Raw Blame History