Given a string column with a value similar to /123/12/34/56/5/, what is the optimal way of querying for all the records that include the given number (12 for example)?
The solution from top of my head is:
SELECT id FROM things WHERE things.path LIKE '%/12/%'
But AFAIK this query can't use indexes on the column due to the leading %.
There must be something better. What is it?
Using PostgreSQL, but would prefer the solution that would work across other DBs too.
If you're happy turning that column into an array of integers, like:
'/123/12/34/56/5/' becomes ARRAY[123,12,34,56,5]
So that path_arr is a column of type INTEGER[], then you can create a GIN index on that column:
CREATE INDEX ON things USING gin(path_arr);
A query for all items containing 12 then becomes:
SELECT * FROM things WHERE ARRAY[12] <@ path_arr;
Which will use the index. In my test (with a million rows), I get plans like:
EXPLAIN SELECT * FROM things WHERE ARRAY[12] <@ path_arr;
QUERY PLAN
----------------------------------------------------------------------------------------
Bitmap Heap Scan on things (cost=5915.75..9216.99 rows=1000 width=92)
Recheck Cond: (path_arr <@ '{12}'::integer[])
-> Bitmap Index Scan on things_path_arr_idx (cost=0.00..5915.50 rows=1000 width=0)
Index Cond: ('{12}'::integer[] <@ path_arr)
(4 rows)
LIKE + GIN index as Erwin suggested, just expressed differently.
In PostgreSQL 9.1 you could utilize the pg_trgm module and build a GIN index with it.
CREATE EXTENSION pg_trgm; -- once per database
CREATE INDEX things_path_trgm_gin_idx ON things USING gin (path gin_trgm_ops);
Your LIKE expression can use this index even if it is not left-anchored.
See a detailed demo by depesz here.
Normalize it If you can, though.
select DISTINCT things.id from things inner join thing_paths on thing_path.thing_id = things.id WHERE thing.path LIKE '/12/%'. But at this stage it is more than I ideally want to do.