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title

Python MySQL Join

🎯 한 줄 통찰 (One-line insight)

INNER JOIN silently drops users with no favorite product (Hannah, Michael) — the same rows only reappear if you switch to LEFT JOIN, making the choice of join type directly visible in which rows survive. [S1]

🧠 핵심 개념 (Core concepts)

JOIN via raw SQL — combining users and products tables on users.fav = products.id, executed through the same cursor pattern. [S1]
INNER JOIN (default via JOIN) — only matching rows in both tables; users with no favorite product are excluded. [S1]
LEFT JOIN — keeps ALL users, even those without a matching product (fav is NULL). [S1]
RIGHT JOIN — keeps ALL products, even those no user has favorited. [S1]

🧩 추출된 패턴 (Extracted patterns)

Missing rows are the tell — the source explicitly points out that Hannah and Michael (no favorite product) vanish under INNER/RIGHT JOIN but reappear under LEFT JOIN — a concrete way to verify which join type is actually in effect. [S1]

📖 세부 내용 (Details)

Sample data: users table has fav referencing products.id; some users (Hannah, Michael) have no fav value. [S1]
INNER JOIN: sql = "SELECT users.name AS user, products.name AS favorite FROM users INNER JOIN products ON users.fav = products.id" — excludes users with no favorite. [S1]
LEFT JOIN: same query with LEFT JOIN — includes ALL users, even without a favorite. [S1]
RIGHT JOIN: same query with RIGHT JOIN — includes ALL products, even unfavorited ones; still excludes favorite-less users. [S1]

⚖️ 모순 및 업데이트 (Contradictions & updates)

소스에서 모순되는 정보는 발견되지 않음.

🛠️ 적용 사례 (Applied in summary)

현재 발견된 실제 적용 사례가 없습니다 — SQL Inner/Left/Right Join 챕터에서 이미 배운 동작 차이를 실제 mysql.connector 쿼리로 재확인하는 문서다. [S1]

💻 코드 패턴 (Code patterns)

LEFT JOIN to include unmatched rows (Python):

sql = "SELECT \
  users.name AS user, \
  products.name AS favorite \
  FROM users \
  LEFT JOIN products ON users.fav = products.id"
mycursor.execute(sql)
myresult = mycursor.fetchall()

✅ 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: Python Tutorial
관련 개념: SQL Inner Join, SQL Left Join, SQL Right Join, Python MySQL Select
참조 맥락: SQL JOIN 동작 차이를 mysql.connector로 실증 — 사라지는/나타나는 행으로 join 유형을 검증할 수 있다.

📚 출처 (Sources)

[S1] W3Schools — Python MySQL Join — https://www.w3schools.com/python/python_mysql_join.asp

📝 변경 이력 (Change history)

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

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