database design - PostgreSQL accent + case insensitive search

Question

I'm looking for a way to support with good performances case insensitive + accent insensitive search. Till now we had no issue on this using MSSql server, on Oracle we had to use OracleText, and now we need it on PostgreSQL.

I've found this post about accent insensitive:
Does PostgreSQL support "accent insensitive" collations?

But we need to combine it with case insensitve. We also need to use indexes, otherwise performances could be impacted. Any real experience about the best approach for large databases?

Answer 1

If you need to "combine with case insensitive", there are a number of options, depending on your exact requirements.

Maybe simplest, make the expression index case insensitive.

Building on the function f_unaccent() laid out in the referenced answer:

• Does PostgreSQL support "accent insensitive" collations?

CREATE INDEX users_lower_unaccent_name_idx ON users(lower(f_unaccent(name)));

Then:

SELECT *
FROM   users
WHERE  lower(f_unaccent(name)) = lower(f_unaccent('Jo?o'));

Or you could build the lower() into the function f_unaccent(), to derive something like f_lower_unaccent().

Or (especially if you need to do fuzzy pattern matching anyways) you can use a trigram index provided by the additional module pg_trgm building on above function, which also supports ILIKE. Details:

• LOWER LIKE vs iLIKE

I added a note to the referenced answer.

Or you could use the additional module citext:

• Deferrable, case-insensitive unique constraint