CS-Notes/notes/Leetcode-Database 题解.md

• 175. Combine Two Tables
• 未完待续...

175. Combine Two Tables

https://leetcode.com/problems/combine-two-tables/description/

Describe

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.

取出 FirstName, LastName, City, State 数据，而不管一个用户有没有填地址信息。

SQL Schema

CREATE TABLE Person ( PersonId INT, FirstName VARCHAR ( 255 ), LastName VARCHAR ( 255 ) );
CREATE TABLE Address ( AddressId INT, PersonId INT, City VARCHAR ( 255 ), State VARCHAR ( 255 ) );
TRUNCATE TABLE Person;
INSERT INTO Person ( PersonId, LastName, FirstName )
VALUES
    ( 1, 'Wang', 'Allen' );
TRUNCATE TABLE Address;
INSERT INTO Address ( AddressId, PersonId, City, State )
VALUES
    ( 1, 2, 'New York City', 'New York' );

Solution

使用左外连接。

SELECT FirstName, LastName, City, State
FROM Person AS p LEFT JOIN address AS a
ON p.PersonId = a.PersonId;

未完待续...