[LeetCode] Combine Two Tables 聯合兩表

 

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還出了是來到數據庫的題，來那么也來做做吧，這道題是第一道，相對來說比較簡單，是一道兩表聯合查找的問題，我們需要用到Join操作，關於一些Join操作可以看我之前的博客SQL Left Join, Right Join, Inner Join, and Natural Join 各種Join小結，最直接的方法就是用Left Join來做，根據PersonId這項來把兩個表聯合起來：

 

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時，我們也可以使用關鍵Using來聲明我們相用哪個列名來進行聯合：

 

解法二：

SELECT Person.FirstName, Person.LastName, Address.City, Address.State FROM Person LEFT JOIN Address USING(PersonId);

 

或者我們可以加上Natural關鍵字，這樣我們就不用聲明具體的列，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;

 

參考資料：

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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