Given an XML document, write a SQL query to find all the nodes with a given attribute value.
Given a table of products and their prices, write a SQL query to find the products with the highest price per unit.
This technical problem involves writing a SQL query to find the average price of all products in a database. An example product table is provided, and the expected output is the average price of all products in the table.
To get customers who have made a purchase in the last 30 days, write a SQL query that returns all customers with a purchase_date within the last 30 days.