[LeetCode][MySQL] 175. Recyclable and Low Fat Products

Easy 🔗175. Combine Two Tables

📝문제 요약

Table: Person

+-------------+---------+
| Column Name | Type    |
+-------------+---------+
| personId    | int     |
| lastName    | varchar |
| firstName   | varchar |
+-------------+---------+
personId is the primary key (column with unique values) for this table.
This table contains information about the ID of some persons and their first and last names.

Table: Address

+-------------+---------+
| Column Name | Type    |
+-------------+---------+
| addressId   | int     |
| personId    | int     |
| city        | varchar |
| state       | varchar |
+-------------+---------+
addressId is the primary key (column with unique values) for this table.
Each row of this table contains information about the city and state of one person with ID = PersonId.

Write a solution to report the first name, last name, city, and state of each person in the Person table. If the address of a personId is not present in the Address table, report null instead.

Return the result table in any order.

The result format is in the following example.

Example 1:

Input:
Person table:
+----------+----------+-----------+
| personId | lastName | firstName |
+----------+----------+-----------+
| 1        | Wang     | Allen     |
| 2        | Alice    | Bob       |
+----------+----------+-----------+
Address table:
+-----------+----------+---------------+------------+
| addressId | personId | city          | state      |
+-----------+----------+---------------+------------+
| 1         | 2        | New York City | New York   |
| 2         | 3        | Leetcode      | California |
+-----------+----------+---------------+------------+
Output:
+-----------+----------+---------------+----------+
| firstName | lastName | city          | state    |
+-----------+----------+---------------+----------+
| Allen     | Wang     | Null          | Null     |
| Bob       | Alice    | New York City | New York |
+-----------+----------+---------------+----------+
Explanation:
There is no address in the address table for the personId = 1 so we return null in their city and state.
addressId = 1 contains information about the address of personId = 2.

✏️문제 풀이

SELECT

SELECT firstName, lastName, city, state

• firstName : 이름
• lastName : 성
• city : 도시
• state : 상태

FROM

FROM Person p LEFT JOIN Address a ON p.personId = a.personId

• Person 테이블과 Address 테이블을 LEFT JOIN
• 두 테이블의 외래키는 personId

💯제출 코드

SELECT firstName, lastName, city, state
FROM Person p LEFT JOIN Address a ON p.personId = a.personId