SQL實(shí)現(xiàn)LeetCode(175.聯(lián)合兩表)

[LeetCode] 175.Combine Two Tables 聯(lián)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(lái)到數(shù)據(jù)庫(kù)的題，來(lái)那么也來(lái)做做吧，這道題是第一道，相對(duì)來(lái)說(shuō)比較簡(jiǎn)單，是一道兩表聯(lián)合查找的問(wèn)題，我們需要用到Join操作，關(guān)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 各種Join小結(jié)，最直接的方法就是用Left Join來(lái)做，根據(jù)PersonId這項(xiàng)來(lái)把兩個(gè)表聯(lián)合起來(lái)：

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(shí)，我們也可以使用關(guān)鍵Using來(lái)聲明我們相用哪個(gè)列名來(lái)進(jìn)行聯(lián)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(guān)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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