leetcode 力扣数据库题175. 组合两个表，左外连接

使用左连接，以左表为基础，若右表中没有对应数据，则显示为NULL

175. 组合两个表

难度简单1047

SQL架构

表1: Person

+-------------+---------+
| 列名         | 类型     |
+-------------+---------+
| PersonId    | int     |
| FirstName   | varchar |
| LastName    | varchar |
+-------------+---------+
PersonId 是上表主键

表2: Address

+-------------+---------+
| 列名         | 类型    |
+-------------+---------+
| AddressId   | int     |
| PersonId    | int     |
| City        | varchar |
| State       | varchar |
+-------------+---------+
AddressId 是上表主键

编写一个 SQL 查询，满足条件：无论 person 是否有地址信息，都需要基于上述两表提供 person 的以下信息：

FirstName, LastName, City, State

# Write your MySQL query statement below
select FirstName, LastName, City, State
from Person LEFT join Address on Person.PersonId=Address.PersonId

 知识拓展

内连接
SELECT O.ID,O.ORDER_NUMBER,C.ID,C.NAME
FROM CUSTOMERS C INNER JOIN ORDERS O ON C.ID=O.CUSTOMER_ID;


左连接
LEFT  JOIN或LEFT OUTER JOIN

右连接
 RIGHT  JOIN 或 RIGHT  OUTER  JOIN

标签：City,JOIN,左外,+-------------+---------+,PersonId,力扣,varchar,175,ID
来源： https://blog.csdn.net/m0_46630679/article/details/123179953