Aggregation Pipeline Operators

The aggregation pipeline processes documents through a sequence of stages — $match, $group, $project, $sort, $lookup — like a data processing pipeline.

db.orders.aggregate([
  { $match: { status: 'shipped' } },
  { $group: { _id: '$customerId', total: { $sum: '$amount' } } },
  { $sort: { total: -1 } },
  { $limit: 5 },
]);

$match — filter documents (like a WHERE clause)
$group — aggregate values per key (like GROUP BY)
$project — reshape documents, include/exclude/compute fields
$lookup — join data from another collection