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

问题

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?

回答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';

回答2:

According to the docs you can do this:

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

回答3:

CREATE UNIQUE INDEX my_index_name ON my_table (LOWER(my_field));

回答4:

You can also use this for wildcard searches:

CREATE INDEX IF NOT EXISTS foo_table_bar_field ON foo_table(lower(username))

Query like so:

SELECT * FROM foo_table WHERE lower(username) like 'bob%'

来源：https://stackoverflow.com/questions/3980050/how-do-i-create-an-index-in-postgresql-based-on-lowercase-only