What index types should I know?

Definition:

MongoDB offers different index types because equality lookup, array search, text search, uniqueness and expiry have different needs. A compound index orders several fields together, while a partial index includes only documents matching a condition. TTL indexes support eventual cleanup rather than precise scheduling.

Key points:

• Single-field: one field; compound: multiple fields; multikey: array values.

• Unique: prevents duplicate indexed values; partial: indexes only matching documents.

• Text: word search; TTL: expires documents asynchronously, not at an exact second.

• A unique index has specific behavior for missing/null fields and arrays, so test it against the actual optional-field model.

Interview point:

• Choose an index from a query or data rule; do not add every index type just because it exists.