$lookup

Lesson in the MongoDB Roadmap · Stage 9: Developer Tools

Last updated 14 September 2026

What is $lookup?

The $lookup aggregation stage performs left outer joins between collections, similar to SQL JOINs. It adds an array field containing matching documents from the "joined" collection based on specified local and foreign fields. $lookup supports pipeline-based lookups for complex matching conditions and enables denormalization of related data for efficient querying and reporting.

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Free resources to learn $lookup

Official docs$lookup
Official docsAggregation Operators

$lookup: common questions

Can I learn $lookup in Hindi?

This lesson is written in English. Once you sign in, open it in the interactive course and ask the AI tutor to explain $lookup in Hindi or Hinglish. The tutor answers from this lesson’s own text, so it stays on the syllabus, and it runs on your own Google, OpenAI or Anthropic key.

Is this $lookup tutorial for beginners?

It is lesson 84 of 106 in the free MongoDB roadmap, in stage 9, Developer Tools. If you are new to MongoDB, start from stage 1 and come back here in order; if you already know the earlier stages, this lesson stands on its own.