Combine Two Tables
来源：程序员人生 发布时间：2015-06-23 08:40:29 阅读次数：3070次
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，由于不管addressid是不是存在，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1致就是。
ON 就没那末智能，你必须指明要关联的表和字段名。
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