Mastering SQL Joins and Window Functions with Real Examples

If you have been writing SQL for a while, you have probably come across joins and window functions . These two features appear in a large percentage of real-world SQL queries, and for good reason. They are among the most powerful tools SQL has to offer. However, they can be confusing at first. Understanding how tables connect with joins and how window functions analyze data across rows is a key step in becoming comfortable with SQL. In this article, we will walk through the most common types of joins using a simple example and explain how they work. 1. What are Joins? In SQL, joins are used to combine rows from two or more tables based on a related column between them. Think of it as sliding two spreadsheets together so that matching values line up, the join type determines what you do with rows that have no partner on the other side. To understand joins better, we will use the following two tables. In the Customers table, customer_id is the primary key . In the Orders table, order_id