[LeetCode] Combine Two Tables

문제 : https://leetcode.com/problems/combine-two-tables/description/

 

풀이:

# 방법1. LEFT JOIN (가장 일반적인 방법)
SELECT 
	p.firstName, p.lastName, a.city, a.state
FROM 
	person p
LEFT JOIN 
	address a
ON 
	p.personId = a.personId;


# 방법2. COALESCE (lEFT JOIN 과 효율성 동일 단지 결과 가공용)
SELECT 
    p.firstName, 
    p.lastName,
    COALESCE(a.city, NULL ) AS city, 
    COALESCE(a.state, NULL ) AS state
FROM 
    Person p
LEFT JOIN 
    Address a
ON 
    p.personId = a.personId;



# 방법3. NATURAL JOIN (실무에서 사용 못함) 
# ON p.personId = a.personId 같은 명시적인 조건 없음
SELECT 
	p.firstName, p.lastName, a.city, a.state
FROM 
	person p
NATURAL JOIN 
	address a;