175. Combine Two Tables

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:

FirstName, LastName, City, State

这里要求不论Address信息有没有都要保留Person的信息，这里是left join.

select Person.FirstName, Person.LastName, Address.City, Address.State from Personleft join Addresson Person.PersonId=Address.PersonId;

SQL 连接：

1. INNER JOIN：如果表中有至少一个匹配，则返回行；

2. LEFT JOIN：即使右表中没有匹配，也从左表返回所有的行；

3. RIGHT JOIN：即使左表中没有匹配，也从右表返回所有的行

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