MongoDB MongoDB Aggregation Framework 1

Question 1

Which aggregation stage filters documents to pass only those matching specified conditions to the next stage?

Accepted Answer

$match

Answer

$match acts like a WHERE clause, filtering documents based on specified criteria before passing them to the next pipeline stage.

Question 2

What is the primary purpose of the $group stage in aggregation?

Accepted Answer

To group documents by a specified identifier and compute aggregate values

Answer

$group groups input documents by a specified _id expression and can apply accumulator expressions like $sum and $avg.

Question 3

Which aggregation accumulator returns the sum of numeric values in a group?

Accepted Answer

$sum

Answer

$sum returns the sum of all numeric values, and when used as $sum: 1, it counts the number of documents in the group.

Question 4

What does the $project stage do in an aggregation pipeline?

Accepted Answer

Passes documents with requested fields to the next stage

Answer

$project reshapes each document by including, excluding, or adding fields before passing documents to the next stage.

Question 5

Which stage limits the number of documents passed to the next aggregation stage?

Accepted Answer

$limit

Answer

$limit passes only the specified number of documents to the next stage, useful for top-N queries.

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