PostgreSQL - Return type and EXECUTE QUERY

Question

My function returns a setof composite type, however the RETURN EXECUTE seems to return some other unknown type:

create type core.search_result as (
  user_id uuid,
  country core.country,
  ethnicity core.ethnicity,
  is_smoker core.smoking_status,
  existing_conditions varchar[]
);

create or replace function core.search_samples(
  country core.country,
  ethnicity core.ethnicity,
  is_smoker core.smoking_status,
  existing_conditions varchar[]
) returns setof core.search_result as $$
  declare
   _where text;
   _sql text := '
     select (
       core.user.id,
       core.user.country,
       core.health_wellness.ethnicity,
       core.health_wellness.is_smoker,
       core.health_wellness.existing_conditions
     )::core.search_result
     from
       core.user
     join
       core.health_wellness
     on
       (core.user.id = core.health_wellness.user_id)';
    results core.search_result[];
  begin
    _where := concat_ws(
      ' AND ',
      CASE WHEN country IS NOT NULL THEN 'core.user.country = $1' END,
      CASE WHEN ethnicity IS NOT NULL THEN 'core.health_wellness.ethnicity = $2' END,
      CASE WHEN is_smoker IS NOT NULL THEN 'core.health_wellness.is_smoker = $3' END
    );
    raise notice '_where: %', _where;
    IF _where <> '' THEN
      _sql := _sql || ' WHERE ' || _where;
      return query EXECUTE _sql
      USING $1, $2, $3;
    end if;
    raise notice 'all input params null';
  end;
$$ language plpgsql stable;

When I try to run the function:

select core.search_samples('United Kingdom', null, null, null);

I get the following error:

NOTICE:  _where: core.user.country = $1
ERROR:  structure of query does not match function result type
DETAIL:  Returned type core.search_result does not match expected type uuid in column 1.
CONTEXT:  PL/pgSQL function core.search_samples(core.country,core.ethnicity,core.smoking_status,character varying[]) line 29 at RETURN QUERY

Answer 1

It's a mismatch of nesting levels.

The return type of the function is declared as:

returns setof core.search_result

core.search_result being the composite type you created earlier. This is equivalent to the more explicit declaration:

RETURNS TABLE (
  user_id uuid,
  country core.country,
  ethnicity core.ethnicity,
  is_smoker core.smoking_status,
  existing_conditions varchar[]
)

Then you return values with:

select (
       core.user.id,
       core.user.country,
       core.health_wellness.ethnicity,
       core.health_wellness.is_smoker,
       core.health_wellness.existing_conditions
     )::core.search_result
     from ...

... which would seem to make sense on a first glance. But the expression is exactly 1 column of type core.search_result, which Postgres tries to fit into the first column of the return type (user_id uuid). Hence the DETAIL information in your error message:

Returned type core.search_result does not match expected type uuid in column 1

You need to return 5 separate columns.

Just remove parentheses & cast:

select core.user.id,
       core.user.country,
       core.health_wellness.ethnicity,
       core.health_wellness.is_smoker,
       core.health_wellness.existing_conditions
     from ...

You may have to add casts to individual columns if data types don't match. One way to avoid that would be to cast the whole ROW type and decompose to separate columns again:

select ((
       core.user.id,
       core.user.country,
       core.health_wellness.ethnicity,
       core.health_wellness.is_smoker,
       core.health_wellness.existing_conditions
     )::core.search_result).*
     from ...

But I'd rather avoid that complication.

---

Aside:
Once you have fixed the exception, raise notice at the very end of your function is reached unconditionally and incorrect. RETURN QUERY ... does not end a function. Only RETURN; does. Rearrange to something like:

IF _where <> '' THEN
  _sql := _sql || ' WHERE ' || _where;
  return query EXECUTE _sql
  USING $1, $2, $3;
ELSE                                     -- !!    
  raise notice 'all input params null';  -- !!
END IF;

Details:

• PostgreSQL stored procedure to return rows or empty set