[LeetCode] 175. Combine Two Tables

原创于 2017-03-11 00:47:42 发布 · 289 阅读

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本文提供了三种不同的左连接示例：标准左连接、使用关键字的左连接及自然左连接，并解释了如何通过这些连接来获取即使没有对应地址信息也能包含所有人的记录。

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Problem

About:
LEFT JOIN, LEFT JOIN USING and NATURAL LEFT JOIN

Solution:
1.

SELECT FirstName, LastName, City, State
FROM Person
LEFT JOIN Address
ON Person.PersonId = Address.PersonId;

SELECT FirstName, LastName, City, State
FROM Person
LEFT JOIN Address
USING(PersonId);

SELECT FirstName, LastName, City, State
FROM Person
NATURAL LEFT JOIN Address;

Note:
left join regardless whether there is an address for each of those people.
So we cannot use “WHERE” here(“WHERE” is used for inner join).