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

# Write your MySQL query statement below
#分析，由于无论addressid是否存在，都要打印，所以是左外连接
select p.firstname,p.lastname,a.city,a.state from Person p left outer join Address a on p.personid=a.personid;

select p.firstname,p.lastname,a.city,a.state from Person p left outer join Address a using(personid);

这两条语句都是可以的

USING "知道" personid 字段在两个表中都有，所以没有指定确切的表都没关系，两个值必须一致就是。

ON 就没那么智能，你必须指明要关联的表和字段名。

Combine Two Tables

原文：http://blog.csdn.net/havedream_one/article/details/45393597