Learn MongoDB

How MongoDB stores data, and how to read it back.

Comparison, set membership, and boolean logic inside a filter.

Dot notation, matching array contents, and the trap everyone hits.

sort(), limit(), skip() — and why skip() stops working at scale.

$set, $inc, upsert, replaceOne — and the update that silently deletes fields.

$push, $addToSet, $pull, and editing an object inside an array.

Stages, order, and reshaping documents with $match and $project.

$group, $sum, $avg, $min, $max, $first — turning many documents into few.

$unwind: one document per array element, and the pattern it unlocks.

The basic join, the pipeline form, and what it costs.

$filter, $map, $reduce, $cond, $ifNull — working inside a document, not across documents.

$facet for dashboards and paging, date grouping, and one end-to-end interview problem.