In which areas did you analyze SQL query execution plans to optimize their efficiency?

Analysis of SQL query execution plans was often used in the following areas:

• Optimizing slow queries in PostgreSQL and MySQL databases. Using EXPLAIN and EXPLAIN ANALYZE, I studied which indexes are used, where full table scans occur, and identified bottlenecks.
• Optimizing queries in reporting systems, where complex JOINs and aggregations led to long execution times.
• In projects with large volumes of data, to minimize response time and load on the database server.

Example: when analyzing a query plan with a JOIN, I found that there was no index on the join key, which led to a full table scan. Adding an index significantly sped up the execution.