Have you used EXPLAIN for query optimization? What did you learn and how much did you manage to speed up the queries?

Yes, EXPLAIN is a tool for analyzing the execution plan of an SQL query, which helps understand how the database management system processes the query.

Using EXPLAIN, you can find out:

• Which indexes are used or not used.
• The sequence of operations (table scans, joins).
• The estimated cost and number of rows processed at each step.

In practice, analysis of EXPLAIN revealed that queries did not use indexes due to incorrect conditions in WHERE or JOIN. After adding the necessary indexes and optimizing conditions, the queries were accelerated by 2-5 times.

Example of using EXPLAIN in PostgreSQL:

EXPLAIN ANALYZE SELECT * FROM users WHERE email = 'example@example.com';

This will show a detailed plan and execution time, helping to identify bottlenecks and optimize the query.