Question

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.

Answer 1

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.