What methods will you use to analyze and optimize a long and resource-intensive SQL query in a database?

The following methods are usually used for analyzing and optimizing long and resource-intensive SQL queries:

1. EXPLAIN / EXPLAIN ANALYZE — obtain the execution plan of the query, understand which operations take the most time and resources.
2. Indexing — check if indexes are used, and add missing ones to speed up searches.
3. Join optimization — check the order and types of joins, possibly replace JOIN with a subquery or vice versa.
4. Query simplification — remove unnecessary fields, conditions, subqueries, and use aggregations efficiently.
5. Profiling — use built-in DBMS tools or external tools to monitor load.
6. Result caching — if data does not change often, cache the query results.

Example of using EXPLAIN in PostgreSQL:

EXPLAIN ANALYZE SELECT * FROM orders o JOIN customers c ON o.customer_id = c.id WHERE o.amount > 1000;

This will show how long each part of the query takes and help identify bottlenecks.