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Introduction
Total revenue for multiple periods
Calculating deltas
Creating "revenue in quarters" reports
Summary

## Instruction

Well done! Let's try another exercise.

## Exercise

Calculate the total monthly revenue for each month of 2017, along with the revenue change as compared to the previous month. Show three columns: RevenueMonth, TotalRevenue, and Delta.

In the first row, leave the delta value as NULL. Order the rows by month.

### Stuck? Here's a hint!

Use the following expression to calculate the delta:

SUM(Amount) - LAG(SUM(Amount), 1) OVER (ORDER BY DATEPART(Month, OrderDate)) AS Delta