Use Partial Indexes for Filtered Queries

Partial indexes only include rows matching a WHERE condition, making them smaller and faster when queries consistently filter on the same condition.

Incorrect (full index includes irrelevant rows):

-- Index includes all rows, even soft-deleted ones
create index users_email_idx on users (email);

-- Query always filters active users
select * from users where email = '[email protected]' and deleted_at is null;

Correct (partial index matches query filter):

-- Index only includes active users
create index users_active_email_idx on users (email)
where deleted_at is null;

-- Query uses the smaller, faster index
select * from users where email = '[email protected]' and deleted_at is null;

Common use cases for partial indexes:

-- Only pending orders (status rarely changes once completed)
create index orders_pending_idx on orders (created_at)
where status = 'pending';

-- Only non-null values
create index products_sku_idx on products (sku)
where sku is not null;

Reference: Partial Indexes