Hello.
As I know 'lhs % rhs' is equivalent to 'similarity(lhs, rhs) >=
show_limit()'.
And so your query should looks like this:
SELECT * FROM restaurants WHERE city % 'warsw';
And it should use index.
On 03.06.2016 13:35, Greg Navis wrote:
Hey!
I'm playing with pg_trgm. It seems that `lhs % rhs` is _almost_
equivalent to `similarity(lhs, rhs) < show_limit()`. The difference that
I noticed is that `%` uses a GIN index while `similarity` does not.
```
grn=# \d restaurants
Table "public.restaurants"
Column | Type | Modifiers
--------+------------------------+-----------
city | character varying(255) | not null
Indexes:
"restaurants_city_trgm_idx" gin (city gin_trgm_ops)
grn=# SELECT COUNT(*) FROM restaurants;
count
--------
515475
(1 row)
Time: 45.964 ms
grn=# EXPLAIN ANALYZE SELECT * FROM restaurants WHERE similarity(city,
'warsw') > show_limit();
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------
Seq Scan on restaurants (cost=0.00..11692.81 rows=171825 width=10)
(actual time=16.436..665.062 rows=360 loops=1)
Filter: (similarity((city)::text, 'warsw'::text) > show_limit())
Rows Removed by Filter: 515115
Planning time: 0.139 ms
Execution time: 665.105 ms
(5 rows)
Time: 665.758 ms
```
My question is: is it possible to make `similarity` use the index? If
not, is there a way to speed up the query above?
Best regards
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Greg Navis
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