docs/content/v2024.2/explore/ycql-language/indexes-constraints/_index.md
As with tables, indexes in YugabyteDB are stored in a distributed manner - that is, they are split into tablets and replicated. Updates to indexes are transactional, which means that row updates and the corresponding index updates occur as a single transaction. Similar to tables, they are stored in LSM format.
{{<note>}} The sharding of indexes is based on the primary key of the index and is independent of how the main table is sharded/distributed. Indexes are not colocated with the base table. {{</note>}}
The YCQL API supports most of the Cassandra index semantics while incorporating other improvements.
The following table lists different types of indexes and their support in YCQL.
| Type | Description | |
|---|---|---|
| {{<icon/yes>}} | Primary key | Unique key that identifies the row |
| {{<icon/no>}} | Foreign key | Link to a column in another table |
| {{<icon/yes>}} | Secondary index | Index on columns other than the primary key |
| {{<icon/yes>}} | Unique index | Set one or many columns to be unique |
| {{<icon/yes>}} | Multi-column index | Index on multiple columns for faster scan with lesser rows |
| {{<icon/yes>}} | Partial index | Indexes that apply to only some rows of the table |
| {{<icon/yes>}} | Covering index | Store other columns in the index for faster retrieval |
| {{<icon/no>}} | Expression index | Index based on a functional operation on columns |
| {{<icon/no>}} | GIN index | Generalized inverted index for fast text search |
| {{<icon/no>}} | GIST Index | For spatial search. Tracked - {{<issue 1337>}} |
{{<index/block>}}
{{<index/item title="Primary keys" body="Explore the use of primary keys in YCQL." href="primary-key-ycql/" icon="fa-thin fa-bars">}}
{{<index/item title="Secondary and multi-column indexes" body="Explore indexes to optimize your database performance with examples." href="secondary-indexes-ycql/" icon="fa-thin fa-list-ol">}}
{{<index/item title="Unique indexes" body="Explore unique indexes in YCQL with examples." href="unique-index-ycql/" icon="fa-thin fa-bars-staggered">}}
{{<index/item title="Partial indexes" body="Explore partial indexes in YCQL with examples." href="partial-index-ycql/" icon="fa-thin fa-list-check">}}
{{<index/item title="Covering indexes" body="Explore Covering indexes in YCQL with examples." href="covering-index-ycql/" icon="fa-thin fa-table-list">}}
{{<index/item title="Secondary indexes with JSONB" body="Create covering and partial indexes with JSONB columns." href="secondary-indexes-with-jsonb-ycql/" icon="fa-thin fa-list-ol">}}
{{</index/block>}}