Why aggregation operators matter in MongoDB - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to calculate the total number of documents in the collection.

MongoDB

db.sales.aggregate([{ $group: { _id: null, total: { $[1]: 1 } } }])

Drag options to blanks, or click blank then click option'

Asum

Bcount

Cavg

Dmax

Attempts:

3 left

💡 Hint

Common Mistakes

Using $count inside $group is invalid.

Using $avg or $max will not count documents.

The $sum operator adds values together. Here, it counts each document by adding 1 for each.

2fill in blank

medium

Complete the code to find the average price of all products.

MongoDB

db.products.aggregate([{ $group: { _id: null, averagePrice: { $[1]: "$price" } } }])

Drag options to blanks, or click blank then click option'

Amax

Bsum

Cmin

Davg

Attempts:

3 left

💡 Hint

Common Mistakes

Using $sum will give total, not average.

Using $min or $max will give smallest or largest value, not average.

The $avg operator calculates the average of the specified field values.

3fill in blank

hard

Fix the error in the aggregation to find the maximum score.

MongoDB

db.scores.aggregate([{ $group: { _id: null, maxScore: { $[1]: "$score" } } }])

Drag options to blanks, or click blank then click option'

Amax_value

BmaxScore

Cmax

Dmaximum

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'maximum' or 'maxScore' as operator names causes errors.

Misspelling the operator leads to failure.

The correct operator to find the maximum value is $max. Other options are invalid.

4fill in blank

hard

Fill both blanks to calculate the total sales and average quantity.

MongoDB

db.orders.aggregate([{ $group: { _id: "$product", totalSales: { $[1]: "$amount" }, averageQty: { $[2]: "$quantity" } } }])

Drag options to blanks, or click blank then click option'

Asum

Bavg

Cmax

Dmin

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up $sum and $avg operators.

Using $max or $min instead of sum or average.

$sum adds all amounts for total sales, and $avg calculates the average quantity.

5fill in blank

hard

Fill all three blanks to group by category, count items, and find max price.

MongoDB

db.items.aggregate([{ $group: { _id: "$category", count: { $[1]: 1 }, maxPrice: { $[2]: "$price" }, minPrice: { $[3]: "$price" } } }])

Drag options to blanks, or click blank then click option'

Asum

Bmax

Cmin

Davg

Attempts:

3 left

💡 Hint

Common Mistakes

Using $avg instead of $sum for counting.

Confusing $max and $min operators.

$sum counts items by adding 1 each, $max finds the highest price, and $min finds the lowest price.