How to effectively identify inefficient SQL queries?

Several approaches are used for effective identification of inefficient SQL queries:

1. Query execution monitoring — enabling slow query log in the DBMS to identify queries that run longer than a specified threshold.

2. Using profilers and monitoring tools — such as pg_stat_statements for PostgreSQL, SQL Server Profiler, MySQL Performance Schema, which collect statistics on query frequency and execution time.

3. Analysis of execution plans (EXPLAIN, EXPLAIN ANALYZE) — helps understand how the DBMS executes the query, which indexes are used, whether full table scans or sorts are slowing down execution.

4. Index checks — absence or improper use of indexes often leads to slow queries.

5. Using metrics and APM systems — integration with application monitoring systems (e.g., New Relic, Datadog) to identify bottlenecks.

Example command for analyzing the execution plan in PostgreSQL:

EXPLAIN ANALYZE SELECT * FROM orders WHERE customer_id = 123;

This shows how long each operation takes and helps identify where to optimize the query.