---
id: python-mysql-join
title: "Python MySQL Join"
category: "Programming_Language"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["파이썬 MySQL 조인"]
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: ["python", "mysql", "w3schools", "join", "innerjoin", "leftjoin", "rightjoin"]
raw_sources: ["https://www.w3schools.com/python/python_mysql_join.asp"]
applied_in: []
github_commit: ""
---

# [[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):
```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).