postgres: Composite fulltext / btree index - postgresql

Question

I want to do a fulltext search on one column and sort in a different column. If I index these two columns separately postgres can't use both indexes in this query. Is there a way to create a composite index that could be used in this scenario?

Answer 1

Unfortunately not.
While you can attach scalar columns to a GIN index via the btree_gin contrib module, Postgres can't use a GIN index for sorting. From the docs:
Of the index types currently supported by PostgreSQL, only B-tree can
produce sorted output — the other index types return matching rows in
an unspecified, implementation-dependent order.

Answer 2

I report as answer my previous comment with example on it
In a similar scenario I build a GiST index on a tsvector column and on
another tetxt colum with gist_trgm_ops operator so I actually did a
full-text search with the tsvector column and then ordered on the
other text column with trigram distance value using only one index.
I created an index on "title" and "search":
CREATE INDEX docs_docume_search_title_gist
ON public.docs_document
USING gist
(title COLLATE pg_catalog."default" gist_trgm_ops, search);
In this query the full-text search is on "search" and the ordering is on "title" with trigram:
SELECT "title", ("title" <-> 'json') AS "distance"
FROM "docs_document"
WHERE ("release_id" = 22 AND "search" ## (plainto_tsquery('json')) = true)
ORDER BY "distance" ASC
LIMIT 10
This is the explain:
Limit (cost=0.40..71.99 rows=10 width=29)
Output: title, (((title)::text <-> 'json'::text))
-> Index Scan using docs_docume_search_title_gist on public.docs_document (cost=0.40..258.13 rows=36 width=29)
Output: title, ((title)::text <-> 'json'::text)
Index Cond: (docs_document.search ## plainto_tsquery('json'::text))
Order By: ((docs_document.title)::text <-> 'json'::text)
Filter: (docs_document.release_id = 22)