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SQL实现LeetCode(175.联合两表)

程序员文章站 2022-03-25 14:55:55
[leetcode] 175.combine two tables 联合两表table: person+-------------+---------+| column name | typ...

[leetcode] 175.combine two tables 联合两表

table: person

+-------------+---------+
| column name | type    |
+-------------+---------+
| personid    | int     |
| firstname   | varchar |
| lastname    | varchar |
+-------------+---------+
personid is the primary key column for this table.

table: address

+-------------+---------+
| column name | type    |
+-------------+---------+
| addressid   | int     |
| personid    | int     |
| city        | varchar |
| state       | varchar |
+-------------+---------+
addressid is the primary key column for this table.

write a sql query for a report that provides the following information for each person in the person table, regardless if there is an address for each of those people:

firstname, lastname, city, state

leetcode还出了是来到数据库的题,来那么也来做做吧,这道题是第一道,相对来说比较简单,是一道两表联合查找的问题,我们需要用到join操作,关于一些join操作可以看我之前的博客sql left join, right join, inner join, and natural join 各种join小结,最直接的方法就是用left join来做,根据personid这项来把两个表联合起来:

解法一:

select person.firstname, person.lastname, address.city, address.state from person left join address on person.personid = address.personid;

在使用left join时,我们也可以使用关键using来声明我们相用哪个列名来进行联合:

解法二:

select person.firstname, person.lastname, address.city, address.state from person left join address using(personid);

或者我们可以加上natural关键字,这样我们就不用声明具体的列,mysql可以自行搜索相同的列:

解法三:

select person.firstname, person.lastname, address.city, address.state from person natural left join address;

参考资料:

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