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GROUP

Short Description

Grouping documents

Detailed Description​

In MongoDB explain plans, GROUP is an execution stage that appears when you use the $group stage in your aggregation pipeline.

What does it do?

  • The GROUP stage collects documents together based on a specified key (or keys) and performs operations (like sum, average, count, etc.) on those groups.
  • This is useful for creating summaries, totals, or statistics from your collection.

Example: If you want to count the number of movies released per year, you might use:

db.movies.aggregate([ { $group: { _id: "$year", count: { $sum: 1 } } }])

  • Here, $group organizes your documents by the year field and counts how many movies are in each year.

Summary:

GROUP in an explain plan means MongoDB is combining documents into groups (based on your query) and doing any group-level calculations you asked for.

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