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adding support for DISTINCT ON for postgres DB #206

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@Chengxuan Chengxuan commented Jan 13, 2026 •
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This PR adds support for PostgreSQL's DISTINCT ON clause to the firefly-common library, enabling efficient querying of distinct rows based on specific field combinations. This feature is PostgreSQL-specific and provides a more performant alternative to using GROUP BY or subqueries for deduplication scenarios.

Postgres ONLY

The feature explicitly validates that the database provider is PostgreSQL before applying DISTINCT ON, returning a clear error message for unsupported providers.

Usage Example

filter := queryFactory.NewFilter(ctx).
    DistinctOn("namespace", "type").
    Sort("created").
    And()

results, _, err := collection.GetMany(ctx, filter)

This generates SQL like:

SELECT DISTINCT ON (namespace, type) * 
FROM table 
ORDER BY namespace, type, created

@Chengxuan
adding support for DISTINCT ON for postgres DB
48cd710 
Signed-off-by: Chengxuan Xing <chengxuan.xing@kaleido.io>
@Chengxuan Chengxuan requested a review from a team as a code owner January 13, 2026 12:01
@peterbroadhurst
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peterbroadhurst commented Jan 19, 2026

The Firefly filtering system is very deliberately not-aligned to SQL syntax currently.

There is support in the library for code to use low-level SQL via extensions.

In this case, this seems to be trying to describe to end users of all APIs built on FF-common a new filtering syntax.

So to tackle the decisions around spelling and exposure problem I think we need, a description of the kind of use case that would require this. Maybe a reasoning for why you chose to push it all the way to the external API, and furthermore to make it specific to PostgreSQL (it's not a PSQL specific construct - I'm sure MongoDB and others have similar constructs).

Then if we decide it makes sense to expose:

  1. To all users on all REST APIs with some naming - that would mean updating this PR to cover all the cases
    • The REST filters
    • The API builders (Typescript and Go)
  2. Something very specific to a particular use case - here the question is why the existing extensions didn't help

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@Chengxuan @peterbroadhurst