> ## Documentation Index
> Fetch the complete documentation index at: https://docs.powersync.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Multiple Client Versions

> Handle multiple client app versions that require different output schemas from Sync Streams.

When schema changes are additive, old clients would just ignore the new tables and columns, and no special handling is required. However, in some cases, the schema changes may be more drastic and may need separate Sync Streams (or Sync Rules) based on the client version.

To distinguish between client versions, clients can pass version information to the PowerSync Service. In [Sync Streams](/sync/streams/overview), these are called connection parameters (accessed via `connection.parameter()`). In legacy [Sync Rules](/sync/rules/overview), these are called [client parameters](/sync/rules/client-parameters).

Example to use different table names based on the client's `schema_version`:

<Tabs>
  <Tab title="Sync Streams">
    ```yaml theme={null}
    # Client passes connection params: {"schema_version": <version>}
    streams:
      assets_v1:
        query: SELECT * FROM assets AS assets_v1
               WHERE user_id = auth.user_id()
               AND connection.parameter('schema_version') = '1'

      assets_v2:
        query: SELECT * FROM assets AS assets_v2
               WHERE user_id = auth.user_id()
               AND connection.parameter('schema_version') = '2'
    ```
  </Tab>

  <Tab title="Sync Rules (Legacy)">
    ```yaml theme={null}
    # Client passes in: "params": {"schema_version": <version>}
      assets_v1:
        parameters: SELECT request.user_id() AS user_id
          WHERE request.parameters() ->> 'schema_version' = '1'
        data:
          - SELECT * FROM assets AS assets_v1 WHERE user_id = bucket.user_id

      assets_v2:
        parameters: SELECT request.user_id() AS user_id
          WHERE request.parameters() ->> 'schema_version' = '2'
        data:
          - SELECT * FROM assets AS assets_v2 WHERE user_id = bucket.user_id
    ```
  </Tab>
</Tabs>

<Warning>
  Handle queries based on parameters set by the client with care. The client can send any value for these parameters, so it's not a good place to do authorization. If the parameter must be authenticated, use parameters from the JWT instead.
</Warning>