How does the use of indexes affect the query performance in PostgreSQL?

Indexes in PostgreSQL significantly speed up query execution by allowing quick data retrieval without full table scans (Seq Scan). When an index exists on a column used for filtering or sorting, the database management system (DBMS) can utilize the index structure (e.g., B-tree) for fast access to the relevant rows.

For example, if you have a table with millions of records and you run a query with a WHERE condition on an indexed column, PostgreSQL will quickly find the matching records through the index rather than scanning all rows.

However, indexes occupy additional space and slow down insert, update, and delete operations because the index also needs to be updated. Therefore, it is important to create indexes only on columns that are frequently used in query conditions.

Example of creating an index:

CREATE INDEX idx_users_email ON users(email);

After this, queries with a WHERE condition like email = 'example@example.com' will execute faster.