Parameter queries allow parameters to be defined on a bucket to group data. These queries can use parameters from the JWT (we loosely refer to these as token parameters), such as a user_id, or parameters from clients directly. 
bucket_definitions:
  # Bucket Name
  user_lists:
    # Parameter Query
    parameters: SELECT request.user_id() as user_id
    # Data Query
    data:
      - SELECT * FROM lists WHERE lists.owner_id = bucket.user_id

  user_lists_table:
    # Similar query, but using a table
    # Access can instantly be revoked by deleting the user row/document
    parameters: SELECT id as user_id FROM users WHERE users.id = request.user_id()
    data:
      - SELECT * FROM lists WHERE lists.user_id = bucket.user_id
Available functions in sync rules are:
  1. request.user_id(): Returns the JWT subject, same as request.jwt() ->> 'sub'
  2. request.jwt(): Returns the entire (signed) JWT payload as a JSON string.
  3. request.parameters(): Returns client parameters as a JSON string.
Example usage: 
request.user_id()
request.jwt() ->> 'sub' -- Same as `request.user_id()
request.parameters() ->> 'param' -- Client parameters

-- Some Supabase-specific examples below. These can be used with standard Supabase tokens,
-- for use cases which previously required custom tokens
request.jwt() ->> 'role' -- 'authenticated' or 'anonymous'
request.jwt() ->> 'email' -- automatic email field
request.jwt() ->> 'app_metadata.custom_field' -- custom field added by a service account (authenticated)
A previous syntax for parameter queries used token_parameters. Expand the below for details on how to migrate to the recommended syntax above.

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Filter on additional columns

bucket_definitions:
  admin_users:
    parameters: |
        SELECT id as user_id FROM users WHERE
           users.id = request.user_id() AND
           users.is_admin = true

    data:
      - SELECT * FROM lists WHERE lists.owner_id = bucket.user_id

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Group according to different columns

bucket_definitions:
  primary_list:
    parameters: |
        SELECT primary_list_id FROM users WHERE
           users.id = request.user_id()
    data:
      - SELECT * FROM todos WHERE todos.list_id = bucket.primary_list_id

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Using different tables for parameters

bucket_definitions:
  owned_lists:
    parameters: |
        SELECT id as list_id FROM lists WHERE
           owner_id = request.user_id()
    data:
      - SELECT * FROM lists WHERE lists.id = bucket.list_id
      - SELECT * FROM todos WHERE todos.list_id = bucket.list_id

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Using a join table

In this example, a single query can return multiple sets of bucket parameters for a single user. Keep in mind that the total number of buckets per user should remain limited (< 1,000), so don’t make buckets too granular. 
bucket_definitions:
  user_lists:
    parameters: |
        SELECT list_id FROM user_lists WHERE
           user_lists.user_id = request.user_id()
    data:
      - SELECT * FROM lists WHERE lists.id = bucket.list_id
      - SELECT * FROM todos WHERE todos.list_id = bucket.list_id

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Multiple bucket parameters

Parameter queries may return multiple bucket parameters.
Note that every bucket parameter must be used in every data query.
bucket_definitions:
  owned_org_lists:
    parameters: |
        SELECT id as list_id, org_id FROM lists WHERE
           owner_id = request.user_id()
    data:
      - SELECT * FROM lists WHERE lists.id = bucket.list_id and lists.org_id = bucket.org_id
      - SELECT * FROM todos WHERE todos.list_id = bucket.list_id and todos.org_id = bucket.org_id

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Using multiple parameter queries

Multiple parameter queries can be used in the same bucket definition. It is important in this case that the output columns are exactly the same for each query in the bucket definition, as these define the bucket parameters. 
bucket_definitions:
  user_lists:
    parameters:
      - SELECT id as list_id FROM lists WHERE owner_id = request.user_id()
      - SELECT list_id FROM user_lists WHERE user_lists.user_id = request.user_id()
    data:
      - SELECT * FROM lists WHERE lists.id = bucket.list_id
      - SELECT * FROM todos WHERE todos.list_id = bucket.list_id
Keep in mind that the total number of buckets per user should remain limited (< 1,000), so don’t make buckets too granular.

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Pass parameters from clients

It is possible to pass parameters from clients directly. See client parameters to learn more.

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Global buckets

Global buckets are buckets with no bucket parameters. This means there is a single bucket for the bucket definition. When no parameter query is specified, it is automatically a global bucket. Alternatively, a parameter query with no output columns may be specified to only sync the bucket to a subset of users. 
bucket_definitions:
  global_admins:
    parameters: |
        SELECT FROM users WHERE
           users.id = request.user_id() AND
           users.is_admin = true

    data:
      - SELECT * FROM admin_settings

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Restrictions

Parameter queries are not run directly on a database. Instead, the queries are used to pre-process rows/documents as they are replicated, and index them for efficient use in the sync process. The supported SQL is based on a small subset of the SQL standard syntax. Notable features and restrictions:
  1. Only simple SELECT statements are supported.
  2. No JOIN, GROUP BY or other aggregation, ORDER BY, LIMIT, or subqueries are supported.
  3. For token parameters, only = operators are supported, and IN to a limited extent.
  4. A limited set of operators and functions are supported — see Operators and Functions.