Introduction
Total revenue for multiple periods
Calculating deltas
Creating "revenue in quarters" reports
Instruction
Very good! It's time for an additional exercise.
Exercise
For each year, calculate the count of orders placed in the current year and the count of orders placed in the previous year. Show three columns: order_year, order_count, and previous_year_order_count.
In the first row, leave the previous year value as NULL. Order the rows by year.
Stuck? Here's a hint!
Use the following expression in the last column:
LAG(COUNT(order_id), 1) OVER (ORDER BY EXTRACT(year FROM order_date))
