Feature Request: Support graphql union types

Currently the only method to do query multiple objects in the same time is to define an custom sql function:

CREATE OR REPLACE FUNCTION search(text TEXT)
RETURNS SETOF search_trigger LANGUAGE sql STABLE AS $$
SELECT id, name,height, NULL AS primary_function, NULL AS length, 'human' AS type FROM humans
WHERE (...)
UNION ALL
SELECT id, name, NULL AS height, primary_function, NULL AS length, 'droid' AS type FROM droids
WHERE (...)
UNION ALL
SELECT id, name, NULL AS height, NULL AS primary_function, length,  'starship' AS type FROM starships
WHERE (...)
$$

while in the front end we query the search_trigger

query {
  search(text: "an") {
    __typename
    id
    name
    height
    primary_function
    length
    type
  }
}

While this should work, we have another type search_trigger instead of article and user in the front end, which can cause many inconveniences, e.g. write new interface and types, inconsistency in local store, etc. It will be good to have support for union type so that we can query with:

query {
  search(text: "an") {
    __typename
    ... on Human {
      name
      height
    }
    ... on Droid {
      name
      primaryFunction
    }
    ... on Starship {
      name
      length
    }
  }
}

Database schema in the examples is borrowed from https://graphql.org/learn/schema/#union-types.

[Svarto]

+1, Ran into this limitation as well, would love union type support to be added to Hasura.

[studious]

I was just beginning to lean into Union types heavily in our Rails portion of the graph only to find out Hasura is lacking this support given how coupled it is to the database as source of truth. Union types and Interfaces have started becoming rather helpful. I’d love to see something announced as our plan is to move even more to Hasura.