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

代码如下：

# Write your MySQL query statement below
select FirstName,LastName,City,State from Person left join Address on Person.PersonId=Address.PersonId

SQL LEFT JOIN 关键字

LEFT JOIN 关键字会从左表 (table_name1) 那里返回所有的行，即使在右表 (table_name2) 中没有匹配的行。