leetcode題175 —— 組合兩個表

表1: Person

+-------------+---------+
| 列名         | 類型     |
+-------------+---------+
| PersonId    | int     |
| FirstName   | varchar |
| LastName    | varchar |
+-------------+---------+
PersonId 是上表主鍵

表2: Address

+-------------+---------+
| 列名         | 類型    |
+-------------+---------+
| AddressId   | int     |
| PersonId    | int     |
| City        | varchar |
| State       | varchar |
+-------------+---------+
AddressId 是上表主鍵

編寫一個 SQL 查詢，滿足條件：無論 person 是否有地址信息，都需要基於上述兩表提供 person 的以下信息：

FirstName, LastName, City, State

實現代碼：

-- 方法一：
SELECT  
        t1.FirstName
       ,t1.LastName
       ,t2.City
       ,t2.State
FROM Person t1
LEFT JOIN Address t2 ON t1.PersonId = t2.PersonId


-- 方法二：
select FirstName, LastName, 
(select City from Address where Address.PersonId = Person.PersonId ) as City,
(select State from Address where Address.PersonId = Person.PersonId ) as State 
from Person;

來源：https://leetcode-cn.com/problems/combine-two-tables/