Using Postgres 9.5 GIN indexes and JSONB

Question

I'm trying to create a Postgres GIN index to speed up the following query:

CREATE TABLE foo (
    id serial primary key,
    a jsonb not null
);

insert into foo(a) values
    ('[{"b": "aaa"}, {"b": "ddd"}]'::jsonb),
    ('[{"b": "aaa"}, {"b": "aaa"}]'::jsonb),
    ('[{"b": "aaa"}]'::jsonb),
    ('[{"b": "aaa"}]'::jsonb),
    ('[{"b": "aaa"}]'::jsonb),
    ('[{"b": "bbb"}]'::jsonb),
    ('[{"b": "bbb"}]'::jsonb),
    ('[{"b": "bbb"}]'::jsonb),
    ('[{"b": "ccc"}]'::jsonb),
    ('[]'::jsonb);

select distinct id from (
    select id, jsonb_array_elements(a)->>'b' as b from foo
) t where t.b = 'aaa'

Is such a thing possible in Postgres? I am open to other alternatives as well. Unfortunately, I can't normalize the table, so I'll need to work with the table structure that I already have.

Answer 1

Yes, you can apply a GIN index here but it may not be particularly useful:

CREATE INDEX find_fast_jsonb_value
ON foo USING GIN (a jsonb_path_ops);

Now you still have to search through the arrays for matching key/value pairs. Your query then becomes:

SELECT DISTINCT id
FROM foo, jsonb_array_elements(a) AS t(b)  -- Implicit LATERAL join
WHERE b @> '{"b": "aaa"}';                 -- Comparing json key/values here

This also places the set-returning-function jsonb_array_elements() in the FROM clause, where it belongs.