# Distributed SQL Surface Area

SingleStore supports a large subset of the SQL surface area (The amount of components installed and or configuration options that are enabled.), with the following limitations:

* Reference tables must have explicit primary keys.
* An `AUTO_INCREMENT` column in a distributed table must be a BIGINT. Auto-increment values are monotonically increasing on each aggregator but not consecutive across the cluster.
* Sharded tables do not support unique keys (unless the unique key contains all columns of the shard key).
* Sharded tables do not support `UPDATE` queries that modify the shard key.
* Sharded tables do not support `UPDATE...LIMIT`.

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Modified at: June 22, 2022

Source: [/db/v9.1/introduction/distributed-architecture/distributed-sql-surface-area/](https://docs.singlestore.com/db/v9.1/introduction/distributed-architecture/distributed-sql-surface-area/)

(An index of the documentation is available at /llms.txt)