Database Leetcode Combine Two Tables

题目：

Table:

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:

First Name , Last Name, City, State

题意：

给定两个表person和address，然后需要将此俩表合并，并且题目中说了，不考虑能不能找到每一个人是否有存在城市和州的地址信息。那么从这句话中就可以判断出，需要用到连接，而且是左连接。因为这是将两张表合并，因此，必然是一个连接问题；此外，对于不考虑人的地址信息，那么在合并两表的时候，可以用左连接将右表中不存在的右表数据置为null。

代码如下：

select p.FirstName,p.LastName,a.City,a.State from Person as p left join Address as a on p.PersonId = a.PersonId;