Q17: What are Unique, Sparse, and Partial Indexes?
- Unique Index: Rejects duplicate values for indexed fields.
- Sparse Index: Only indexes documents that actually contain the indexed field (ignores documents missing the key).
- Partial Index: Indexes documents satisfying a specified filter expression (
partialFilterExpression), reducing index memory footprint.
Key Takeaways
- Unique indexes enforce database-level uniqueness.
- Partial indexes save RAM by indexing specific document subsets.
Knowledge Check
Which index type allows unique constraints on optional fields without throwing errors on multiple missing null entries?