题目地址：

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

给定两个表，分别是Person表和Address表：

+-------------+---------+ | Column Name | Type | +-------------+---------+ | PersonId | int | | FirstName | varchar | | LastName | varchar | +-------------+---------+ +-------------+---------+ | Column Name | Type | +-------------+---------+ | AddressId | int | | PersonId | int | | City | varchar | | State | varchar | +-------------+---------+

要求查出每个人的FirstName, LastName, City, State这些信息，并且要保证每个人都被显示出来，无论其PersonId是否出现在Address表里。

可以用LEFT JOIN来做，LEFT JOIN可以保证JOIN的时候，左表的所有行都显示出来。代码如下：

SELECT FirstName, LastName, City, State FROM Person LEFT JOIN Address ON Person.PersonId = Address.PersonId