Day 8 I4G10daysofCodeChallenge

Problem: Given a two SQL tables A,B in a database Combine them. with a common column in A and B and rows that doesn't have a common fields should return null in the B fields.

Table: Person

+-------------+---------+
| 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.

Table: Address

+-------------+---------+
| 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.

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.

Example :

Input:
Person table:
+----------+----------+-----------+
| personId | lastName | firstName |
+----------+----------+-----------+
| 1 | Wang | Allen |
| 2 | Alice | Bob |
+----------+----------+-----------+
Address table:
+-----------+----------+---------------+------------+
| addressId | personId | city | state |
+-----------+----------+---------------+------------+
| 1 | 2 | New York City | New York |
| 2 | 3 | Leetcode | California |
+-----------+----------+---------------+------------+
Output:
+-----------+----------+---------------+----------+
| firstName | lastName | city | state |
+-----------+----------+---------------+----------+
| Allen | Wang | Null | Null |
| Bob | Alice | New York City | New York |
+-----------+----------+---------------+----------+

Solution.

After reading through the solution I understand that what I need to do is to join Table A and B, using the LEFT JOIN.
Such that values that if some Rows in column A don't have the personId in them they should return null in the fields.

SELECT P.lastName, P.firstName, A.city, A.state
FROM Person P LEFT JOIN Address A ON P.personId = A.personId
I read about sql Joins
GeeksforGeeks SQL Join

Joining two tables

Leetcode problem