$group
Reference group: Pipeline stages
What it does
Groups by _id and computes accumulators.
Syntax
{$group: { _id: expression, field: accumulator }}
Use case
Totals, counts, averages, and grouped arrays.
$group: practical example
{ $group: { _id: "$customerId", revenue: { $sum: "$total" }, orders: { $sum: 1 } } }💡 Explanation
Groups by
_id and computes accumulators.
When to use it
Totals, counts, averages, and grouped arrays.Key Takeaways
- Groups by
_idand computes accumulators. - Typical use: Totals, counts, averages, and grouped arrays.