How to tune ilike query involving multiple columns

Question

SELECT * FROM patients WHERE "account_id" = 765 AND first_name ilike 'rahul%';

The query is currently taking 100ms plus, I have individually indexed account_id and first_name. First name is using gist index.

EXPLAIN ANALYZE:

Bitmap Heap Scan on patients  (cost=960.12..29301.39 rows=61 width=117) (actual time=8.399..100.206 rows=11 loops=1)
  Recheck Cond: (account_id = 765)
  Filter: ((first_name)::text ~~* 'rahul'::text)
  Rows Removed by Filter: 28978
  Heap Blocks: exact=8948
  ->  Bitmap Index Scan on index_patients_on_account_id  (cost=0.00..960.11 rows=31424 width=0) (actual time=4.569..4.569 rows=29003 loops=1)
        Index Cond: (account_id = 765)
Planning Time: 0.774 ms
Execution Time: 100.251 ms

I feel I need a multi column index, not sure about how to go about creating it.

Answer 1

If you can rewrite your query using LIKE and lower and if the wildcard is always at the end of the pattern, then the optimal index would probably be:

create index on patients (account_id, lower(first_name) text_pattern_ops)

With a query as:

SELECT * FROM patients
  WHERE "account_id" = 765 AND lower(first_name) like lower('rahul%');

The first lower needs to be there to match the index. The 2nd lower is optional, it can be removed if you know the client will always provide an already lower-case string.