Group active subscriptions by `plan`, calculate total revenue, and sort by revenue descending.

Problem Statement

<p>Group active subscriptions by <code>plan</code>, calculate total revenue, and sort by revenue descending.</p>

Examples

Input: subscriptions collection: +-----+------------+-------+-----------+ | _id | plan | price | status | +-----+------------+-------+-----------+ | 1 | Starter | 29 | active | | 2 | Pro | 99 | active | | 3 | Pro | 99 | active | | 4 | Starter | 29 | cancelled | | 5 | Enterprise | 499 | active | +-----+------------+-------+-----------+

Output: +------------+--------------+ | _id | totalRevenue | +------------+--------------+ | Enterprise | 499 | | Pro | 198 | | Starter | 29 | +------------+--------------+

Explanation: The query retrieves all documents from the collection that satisfy the specified filter criteria.

Complexity

Time Complexity: -

Space Complexity: -

Hints

💡 Hint 1: This problem requires grouping documents by a key and aggregating values. Use db.<collection>.aggregate([...]) with a $group stage. 💡 Hint 2: In the $group stage, set _id to the grouping field (e.g. "$category" or "$dept") and use accumulator operators like $sum, $avg, $max, or $min. 💡 Hint 3: Remember to call .toArray() at the end of the aggregation pipeline to return the resolved documents array.

Editorial & Approach

Problem Overview & Intuition

To solve "Revenue Per Plan Tier", we query the MongoDB document store. The goal is to group active subscriptions by `plan`, calculate total revenue, and sort by revenue descending. Using an aggregation pipeline, the database engine filters and structures the BSON documents efficiently.

Step-by-Step Approach

Identify Target Collection: Access the collection through the db instance.
Construct Query / Pipeline: Build the aggregation stages ($match, $group, $sort, etc.).
Resolve Cursor: Invoke .toArray() to transform the query cursor into the required array of documents.

Optimal Implementation (MongoDB)

function solve(db) {
  return db.subscriptions.aggregate([
    { $match: { status: "active" } },
    { $group: { _id: "$plan", totalRevenue: { $sum: "$price" } } },
    { $sort: { totalRevenue: -1 } }
  ]);
}

Complexity Analysis

Time Complexity O(N) pipeline traversal through aggregation stages.

Space Complexity O(M) intermediate document buffer in aggregation pipeline.

Key Considerations & Edge Cases

Empty Collections: If no documents match, the query cleanly returns an empty array [].
Missing / NULL Fields: Missing fields in documents are handled safely without throwing runtime exceptions.
Type Coercion: BSON types (ObjectId, Numbers, Strings) are compared strictly according to MongoDB specifications.

Revenue Per Plan Tier

Hard

Group active subscriptions by plan, calculate total revenue, and sort by revenue descending.

Example Scenarios

1Example 1

Input:

subscriptions collection

_id	plan	price	status
1	Starter	29	active
2	Pro	99	active
3	Pro	99	active
4	Starter	29	cancelled
5	Enterprise	499	active

Output:

_id	totalRevenue
Enterprise	499
Pro	198
Starter	29

Explanation:

The query retrieves all documents from the collection that satisfy the specified filter criteria.

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Query Results (JSON)

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