[LeetCode] 175.Combine Two Tables 联合两表
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
LeetCode还出了是来到数据库的题，来那么也来做做吧，这道题是第一道，相对来说比较简单，是一道两表联合查找的问题，我们需要用到Join操作，关于一些Join操作可以看我之前的博客SQL Left Join, Right Join, Inner Join, and Natural Join 各种Join小结，最直接的方法就是用Left Join来做，根据PersonId这项来把两个表联合起来：
解法一：
SELECT Person.FirstName, Person.LastName, Address.City, Address.State FROM Person LEFT JOIN Address ON Person.PersonId = Address.PersonId;
在使用Left Join时，我们也可以使用关键Using来声明我们相用哪个列名来进行联合：
解法二：
SELECT Person.FirstName, Person.LastName, Address.City, Address.State FROM Person LEFT JOIN Address USING(PersonId);
或者我们可以加上Natural关键字，这样我们就不用声明具体的列，MySQL可以自行搜索相同的列：
解法三：
SELECT Person.FirstName, Person.LastName, Address.City, Address.State FROM Person NATURAL LEFT JOIN Address;
参考资料：
https://leetcode.com/discuss/21216/its-a-simple-question-of-left-join-my-solution-attached
https://leetcode.com/discuss/53001/comparative-solution-between-left-using-natural-left-join
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原文链接：https://www.cnblogs.com/grandyang/p/5348900.html
