How do I create an index in PostgreSQL based on lowercase only?

Question

How would I set up an index based on lower case only?

Even though the actual field contains both upper and lower case letters.

Also, can I run a query and have only the lower case index value returned?

Answer 1

You can create the index and transform the field to upper- or lower-case. Then when you do your queries, you can do the same transform and it'll do the right thing.

So:

CREATE UNIQUE INDEX lower_case_username ON users ((lower(username))); 

Then query for the same thing:

SELECT username FROM users WHERE lower(username) = 'bob'; 

Answer 2

According to the docs you can do this:

CREATE UNIQUE INDEX lower_title_idx ON films ((lower(title)));