NoSQL map reduce and aggregate quiz

Which command is used to insert a document into a MongoDB collection?

• db.collection.insertDocument()

• db.collection.insert()

• db.collection.add()

• db.insertOne()

Which aggregation stage is used to filter documents?

• $match

• $group

• $sort

• $project

In a map-reduce operation, what is the role of the “map” function?

• Reduces the data

• Filters data based on criteria

• Emits key-value pairs for grouping

• Sorts the data

What MongoDB command is used to run a map-reduce operation?

• db.collection.mapReduce()

• db.runMapReduce()

• db.mapReduce()

• db.collection.reduceMap()

In Map-Reduce, the "reduce" function must:

• Output documents only

• Take a key and an array of values and return a reduced value

• Be written in SQL

• Output a cursor

How do you sort documents by a field named age in descending order using aggregation?

• { $sort: { age: "desc" } }

• { $sort: { age: -1 } }

• { $order: { age: -1 } }

• { $sortBy: { age: -1 } }

How would you calculate the total number of documents in a collection using aggregation?

• { $group: { _id: null, total: { $count: 1 } } }

• { $count: "total" }

• { $sum: "count" }

• { $size: "total" }

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

• Flattens an array field to output a document for each element

• Removes fields from a document

• Converts documents to arrays

• D) Joins collections

What does the db.collection.aggregate() method return?

• A single document

• An array

• A cursor

• A string

What is the correct syntax for emitting a key-value pair in a map function?

• emit(key, value);

• map(key, value);

• send(key, value);

• output(key: value);