Today I Learned

A Hashrocket project

Lower Is Faster Than ilike

There are a couple ways to do a case-insensitive comparison of data in PostgreSQL. One way is to use the ilike operator for comparison. Another way is to use the lower() function on both sides of the = operator for comparison. Using lower() is a bit faster than using ilike.

When comparing

select * from users where email ilike 'some-email@example.com';

to

select * from users where lower(email) = lower('some-email@example.com');

we find (via explain analyze) that using lower() was taking around 12ms where as the ilike example was taking around 17ms.

We earn orders of magnitude in performance when adding a functional index that uses the lower() function like so:

create unique index users_unique_lower_email_idx on users (lower(email));

After adding this index, the example using lower() drops to around 0.08ms.

For the full example and explain analyze outputs, see this document.

Looking for help? Hashrocket developers believe that data quality is as important as code quality. We enjoy all the challenges of relational databases, from finding the fastest index, to structuring data to fit the needs of an application. We're eager to share our experiences; check out PG Casts, a series of free weekly PostgreSQL screencasts.