In MongoDB, the $dayOfMonth aggregation pipeline operator returns the day of the month for a date as a number between 1 and 31.
You can optionally specify a timezone to use for the result.
The $dayOfMonth operator accepts either a date (as either a Date, a Timestamp, or an ObjectId), or a document that specifies the date and timezone to use.
In MongoDB, the $dayOfYear aggregation pipeline operator returns the day of the year for a date as a number between 1 and 366.
You can optionally specify a timezone to use for the result.
The $dayOfYear operator accepts either a date (as either a Date, a Timestamp, or an ObjectId), or a document that specifies the date and timezone to use.
If you’re familiar with SQL, you might know about the UNION clause, which concatenates the results of two queries into a single result set. In particular, UNION ALL includes duplicates.
In MongoDB, we can use the $unionWith aggregation pipeline stage to achieve the same effect that UNION ALL produces. The $unionWith stage performs a union of two collections – it combines pipeline results from two collections into a single result set. And it includes duplicates.
In MongoDB the $sortByCount aggregation pipeline stage groups incoming documents based on the value of a specified expression, then computes the count of documents in each distinct group.
Each group is output in its own document, which consists of two fields:
_id field containing the distinct grouping value, andcount field containing the number of documents belonging to that grouping.The documents are sorted by count in descending order.
In MongoDB the $count aggregation operator passes a document to the next stage in the aggregation pipeline that contains a count of the number of documents input to the current stage.