Exercise 1: Status distribution

Count orders in each status and sort by frequency. Skills: $group, $sum, $sort.

Exercise 2: Customer spending

Calculate delivered item revenue per customer. Create one version excluding discounts and another subtracting each order-level discount once. Skills: $reduce, $group, business rules.

Exercise 3: Product units sold

Calculate quantity sold per product and return the top three. Skills: $match, $unwind, $group, $sort, $limit.

Exercise 4: Monthly order counts

Group by month and year, then compare all statuses with delivered-only orders. Skills: $dateTrunc, $group.

Exercise 5: Customer category diversity

Count distinct categories purchased by each customer and return customers with at least two categories. Skills: $addToSet, $size, $match.

Exercise 6: Product dashboard

Use $facet to return a product list, category counts, and total count.

Exercise 7: Data-quality audit

Convert imported amounts to Decimal128 and count valid and invalid values.

Exercise 8: Top customer per city

Join orders to customers, calculate delivered revenue, and find the highest-spending customer in each city. Define tie handling.

Exercise 9: Moving average

Calculate a moving average over the current and two preceding orders per customer using $setWindowFields.

Exercise 10: Materialized report

Write product summaries to a reporting collection, run the pipeline twice, and verify idempotency and stale-record handling.

Challenge: Explain the cost

Compare execution statistics before and after an appropriate index or pipeline rewrite using realistic data. Report only measured performance changes.