Combine Two Tables Leetcode

最新推荐文章于 2025-11-24 16:32:05 发布

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本文介绍了一个SQL查询案例，该案例使用左连接从Person表中选取所有人员的信息，并尽可能地匹配Address表中的地址详情，即使某些人员没有对应的地址记录。

able: Person

+-------------+---------+
| Column Name | Type    |
+-------------+---------+
| PersonId    | int     |
| FirstName   | varchar |
| LastName    | varchar |
+-------------+---------+
PersonId is the primary key column for this table.

Table: Address

+-------------+---------+
| Column Name | Type    |
+-------------+---------+
| AddressId   | int     |
| PersonId    | int     |
| City        | varchar |
| State       | varchar |
+-------------+---------+
AddressId is the primary key column for this table.

Write a SQL query for a report that provides the following information for each person in the Person table, regardless if there is an address for each of those people:

FirstName, LastName, City, State

这道题目考察的是left join的应用，题目中提到不管有没有地址都从Person中选出来因此考虑用left join 或者right join，返回包含全部Person中的内容以及符合join条件的Address的内容。

如果用right join

# Write your MySQL query statement below
SELECT Person.FirstName,Person.LastName,Address.City,Address.State 
From Address
RIGHT join Person on Person.PersonId=Address.PersonId

如果用left join

# Write your MySQL query statement below
SELECT Person.FirstName,Person.LastName,Address.City,Address.State 
From Person
LEFT JOIN Address on Person.PersonId=Address.PersonId

二者是等价的