Combine Two Tables
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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
# Write your MySQL query statement below#分析,由于无论addressid是否存在,都要打印,所以是左外连接select p.firstname,p.lastname,a.city,a.state from Person p left outer join Address a on p.personid=a.personid;
select p.firstname,p.lastname,a.city,a.state from Person p left outer join Address a using(personid);
这两条语句都是可以的
USING "知道" personid 字段在两个表中都有,所以没有指定确切的表都没关系,两个值必须一致就是。
ON 就没那么智能,你必须指明要关联的表和字段名。
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