Answer
$lookup performs a left outer join between collections, enriching documents with related data.
Quick Answer
$lookup performs a left outer join between collections in an aggregation pipeline. It matches documents from the "from" collection based on a localField/foreignField pair and adds matched docs as an array in the output. Similar to SQL JOIN. Performance tip: $lookup is expensive - consider embedding if you always access data together.
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SugharaIQ Editorial Team
Verified Answer
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Source: SugharaIQ