SQL joins and window functions

Joins and Window Functions Sql joins When working with relational databases, data is usually in different tables .Join functions help in combining 2 or more tables based on a related column between them usually a primary key. Types of Joins Inner Join Left Join Right Join Full join Self Join Inner Join Combines rows that have matching values in both tables. Inner joins only show values that are not null. Example : Suppose we have a customers table with columns (customer_id, first_name, last_name, membership_status) and a sales table with columns (sale_id, customer_id, product_id, sale_date, total_amount). To find customers who made sales and their total purchase amounts: This returns only customers with matching sales records. Left Join A left join Returns all rows from the left table, and only the matched rows from the right table. If there's no match the right table returns null. Example : Using the customers and sales tables, to list all customers and their sales, even if they have