Antigravity Agent
9a135bd19d
최상위 10_Wiki/Topic_*였던 4개 카테고리 폴더를 10_Wiki/Topics/Topic_* 로 재배치. 콘텐츠 변경 없음(순수 폴더 이동) — Topics/ 하위 나머지 폴더는 이미 지난 커밋에서 전부 정리된 상태(잔존 항목은 에이전트 운영 상태 및 사용자가 보존을 요청한 업데이트0615/무제 3.canvas 뿐).
3.5 KiB
3.5 KiB
id, title, category, status, verification_status, canonical_id, aliases, duplicate_of, source_trust_level, confidence_score, created_at, updated_at, review_reason, merge_history, tags, raw_sources, applied_in, github_commit
| id | title | category | status | verification_status | canonical_id | aliases | duplicate_of | source_trust_level | confidence_score | created_at | updated_at | review_reason | merge_history | tags | raw_sources | applied_in | github_commit | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| sql-count | SQL Count | Database | draft | conceptual |
|
B | 0.9 | 2026-07-04 | 2026-07-04 |
|
|
SQL Count
🎯 한 줄 통찰 (One-line insight)
COUNT() behaves differently depending on its argument — COUNT(*) counts all rows including NULLs, COUNT(column) counts non-null values, and COUNT(DISTINCT column) counts unique non-null values. [S1]
🧠 핵심 개념 (Core concepts)
- COUNT() function — returns the number of rows matching a specified criterion. [S1]
- Syntax —
SELECT COUNT([DISTINCT] column_name | *) FROM table_name WHERE condition;. [S1] COUNT(*)— counts the total number of rows, including NULL values. [S1]COUNT(column_name)— counts only non-null values in that column. [S1]COUNT(DISTINCT column_name)— counts only unique, non-null values. [S1]
🧩 추출된 패턴 (Extracted patterns)
- Argument choice changes semantics — the three COUNT variants answer three different questions (total rows / filled-in rows / unique values), so picking the right one matters for correctness, not just style. [S1]
📖 세부 내용 (Details)
- Total row count:
SELECT COUNT(*) FROM Products;. [S1] - Non-null count for a column:
SELECT COUNT(ProductName) FROM Products;. [S1] - Unique non-null count:
SELECT COUNT(DISTINCT Price) FROM Products;. [S1] - With WHERE:
SELECT COUNT(ProductID) FROM Products WHERE Price > 20;. [S1] - With alias:
SELECT COUNT(*) AS [Number of records] FROM Products;. [S1] - With GROUP BY:
SELECT COUNT(*) AS [Number of records], CategoryID FROM Products GROUP BY CategoryID;. [S1]
⚖️ 모순 및 업데이트 (Contradictions & updates)
소스에서 모순되는 정보는 발견되지 않음.
🛠️ 적용 사례 (Applied in summary)
현재 발견된 실제 적용 사례가 없습니다 — SELECT DISTINCT 챕터에서 이미 소개된 COUNT(DISTINCT ...) 패턴이 여기서 정식으로 다뤄진다. [S1]
💻 코드 패턴 (Code patterns)
Three COUNT variants (SQL):
SELECT COUNT(*) FROM Products; -- all rows, incl. NULLs
SELECT COUNT(ProductName) FROM Products; -- non-null values only
SELECT COUNT(DISTINCT Price) FROM Products; -- unique non-null values
✅ 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 Select Distinct, SQL Group By
- 참조 맥락: 행 개수를 세는 모든 리포트의 기본 함수 — DISTINCT와 결합해 고유값 개수도 셀 수 있다.
📚 출처 (Sources)
- [S1] W3Schools — SQL COUNT() Function — https://www.w3schools.com/sql/sql_count.asp
📝 변경 이력 (Change history)
- 2026-07-04: Initial draft synthesized from the W3Schools "SQL COUNT() Function" page (Astra wiki-curation, P-Reinforce v3.1 format).