Joins¶
Joins are best explained using Venn diagrams
Remember that in case of multiple joins each single join produces a single derived table that is then joined to the next table and so on.
Questions¶
Problem: [Leetcode] Join 2 tables
Reference - Leetcode
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
Solution:
select a.FirstName, a.LastName, b.City, b.State
from Person a
left join Address b
on a.PersonId = b.PersonID