leetcode_175_组合两个表[join]

leetcode 175 组合两个表

• 题目

  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
  

• 解

  select FirstName, LastName, City, State
  from Person left outer join Address
  on Person.PersonId = Address.PersonId;
  

  1. join 用于把来自两个或多个表的行结合起来
     • cross join 叉联结
     • inner join 内联结
     • outer join 外联结
       • left outer join或left join 左外联结
       • right outer join或right join 右外联结
       • full outer join或full join 全外联结