You have 100 documents in events collection, each containing an array attendees of 50 elements. 20 of those documents have at least one attendee with "VIP": true. Consider two approaches to count total "VIP" attendees across all events:

Approach A: $unwind the attendees array, then $match "VIP": true.
Approach B: $match documents where at least one attendee is VIP, then $unwind attendees, then $match "VIP": true.

How many documents will be output by the $unwind stage in Approach B?

Question

You have 100 documents in events collection, each containing an array attendees of 50 elements. 20 of those documents have at least one attendee with "VIP": true. Consider two approaches to count total "VIP" attendees across all events: 
 
  Approach A: $unwind the attendees array, then $match "VIP": true. 
  Approach B: $match documents where at least one attendee is VIP, then $unwind attendees, then $match "VIP": true. 
 
  How many documents will be output by the $unwind stage in Approach B?

Answer

50 (one unwound attendee per original doc)

Answer

100 (all documents unwound into attendees)

Answer

1,000 (20 docs × 50 attendees each)

Answer

20 (only VIP attendees produce output)

Crowdly

You have 100 documents in events collection, each containing an array attendees ...

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