How to index a string array column for pg_trgm `'term' % ANY (array_column)` query?

Question

I have tried an ordinary Postgres gin index as well as the pg_trgm gin_trgm_ops and gist_trgm_ops indexes (using this workaround: https://

Answer 1

I created a test table and a function called f that only converts to text.

CREATE OR REPLACE FUNCTION getNArray(el text[], count int) RETURNS text[] AS $$
  SELECT array_agg(el[random()*(array_length(el,1)-1)+1]) FROM generate_series(1,count) g(i)
$$
VOLATILE
LANGUAGE SQL;

DROP TABLE testGin;
CREATE TABLE testGin(id serial PRIMARY KEY, array_column text[]);

WITH t(ray) AS(
  SELECT (string_to_array(pg_read_file('words.list')::text,E'\n')) 
) 
INSERT INTO testGin(array_column)
SELECT getNArray(T.ray, 4) FROM T, generate_series(1,100000);

The cast function:

CREATE OR REPLACE FUNCTION f(arr text[]) RETURNS text AS $$
   SELECT arr::text
 LANGUAGE SQL IMMUTABLE;

CREATE INDEX ON testGin USING GIN(f(array_column) gin_trgm_ops);

The usage with ILIKE:

postgres=# EXPLAIN SELECT id FROM testgin WHERE f(array_column) ilike '%test%';
                                  QUERY PLAN                                   
-------------------------------------------------------------------------------
 Bitmap Heap Scan on testgin  (cost=34.82..1669.63 rows=880 width=4)
   Recheck Cond: (f(array_column) ~~* '%test%'::text)
   ->  Bitmap Index Scan on testgin_f_idx  (cost=0.00..34.60 rows=880 width=0)
         Index Cond: (f(array_column) ~~* '%test%'::text)
(4 rows)

If you want a more accurate search by including the % operator, you can do as bellow. This will scan the index and then, it will apply your filter:

postgres=# explain SELECT id, array_column FROM testgin WHERE 'response' % ANY (array_column) and f(array_column) ~ 'response';
                                  QUERY PLAN                                  
------------------------------------------------------------------------------
 Bitmap Heap Scan on testgin  (cost=76.08..120.38 rows=1 width=85)
   Recheck Cond: (f(array_column) ~ 'response'::text)
   Filter: ('response'::text % ANY (array_column))
   ->  Bitmap Index Scan on testgin_f_idx  (cost=0.00..76.08 rows=11 width=0)
         Index Cond: (f(array_column) ~ 'response'::text)
(5 rows)