版权声明:本文为博主原创文章,未经博主允许不得转载。 https://blog.csdn.net/xnh_565175944/article/details/80635857
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
思路解析:根据题目要求,给出FirstName,LastName,City,State 四个属性,即使为空
所以我们用左外连接,即使地址信息为空也照常输出NULL
代码如下:
select Person.FirstName,Person.LastName,Address.City,Address.State
from Person left join Address on Person.PersonId=Address.PersonId