Доводилось ли работать с планировщиком запросов (EXPLAIN) для оптимизации SQL-запросов?

Yes, I have used the EXPLAIN query planner to analyze and optimize SQL queries.

EXPLAIN shows how the DBMS executes a query: which indexes are used, the order of table scans, join types, and an estimated cost of operations.

In practice, it helps identify bottlenecks, such as:

• Missing index on a column used in WHERE or JOIN.
• Full table scan, which slows down the query.
• Incorrect join order.

Example of usage:

EXPLAIN SELECT * FROM orders WHERE customer_id = 123;

Based on the results, you can add an index:

CREATE INDEX idx_customer_id ON orders(customer_id);

And then check if the query runs faster.

Thus, EXPLAIN is an important tool for understanding and improving query performance.