How to identify the most resource-intensive SQL queries in a database?

To identify the most resource-intensive SQL queries in a database, the following approaches can be used:

• Enable slow query logging in the DBMS to record queries that run longer than a specified threshold.
• Use built-in profiling and monitoring tools of the DBMS, such as EXPLAIN or EXPLAIN ANALYZE in PostgreSQL, to understand the execution plan and estimate costs.
• In systems like MySQL, you can use SHOW PROCESSLIST or Performance Schema to analyze current queries.
• In Python, query profiling can be integrated via ORM (e.g., SQLAlchemy) or middleware that logs query execution times.

Example of using EXPLAIN in PostgreSQL:

EXPLAIN ANALYZE SELECT * FROM orders WHERE customer_id = 123;

This will show how long the query takes and which indexes are used.