Problem#
Table: Person
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+-------------+---------+
| Column Name | Type |
+-------------+---------+
| personId | int |
| lastName | varchar |
| firstName | varchar |
+-------------+---------+
personId is the primary key column for this table.
This table contains information about the ID of some persons and their first and last names.
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Table: Address
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+-------------+---------+
| Column Name | Type |
+-------------+---------+
| addressId | int |
| personId | int |
| city | varchar |
| state | varchar |
+-------------+---------+
addressId is the primary key column for this table.
Each row of this table contains information about the city and state of one person with ID = PersonId.
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Write an SQL query to report the first name, last name, city, and state of each person in the Person table. If the address of a personId is not present in the Address table, report null instead.
Examples#
Example 1:
Input:
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Person table:
+----------+----------+-----------+
| personId | lastName | firstName |
+----------+----------+-----------+
| 1 | Wang | Allen |
| 2 | Alice | Bob |
+----------+----------+-----------+
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Address table:
+-----------+----------+---------------+------------+
| addressId | personId | city | state |
+-----------+----------+---------------+------------+
| 1 | 2 | New York City | New York |
| 2 | 3 | Leetcode | California |
+-----------+----------+---------------+------------+
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Output:
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+-----------+----------+---------------+----------+
| firstName | lastName | city | state |
+-----------+----------+---------------+----------+
| Allen | Wang | Null | Null |
| Bob | Alice | New York City | New York |
+-----------+----------+---------------+----------+
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Explanation:
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There is no address in the address table for the personId = 1 so we return null in their city and state.
addressId = 1 contains information about the address of personId = 2.
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Solution#
Method 1 - Using Left Join#
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SELECT firstName, lastName, city, state
FROM Person p
LEFT JOIN Address a
ON a.PersonId=a.PersonId
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