At what level were indexes developed — up to the level of EXPLAIN plans?

Analyzing indexes at the level of EXPLAIN plans means that during query optimization and database structure tuning, execution plans of queries shown by the EXPLAIN command (or similar tools) are examined.

This allows:

• To understand which indexes are used in queries.
• To identify full table scans instead of index searches.
• To evaluate the cost of operations and select optimal indexes.

In practice, this means that indexes are not just created based on assumptions but are tested for effectiveness through analysis of execution plans for specific queries. This approach helps avoid redundant or inefficient indexes and improves database performance.

For example, if EXPLAIN shows that a query does not use an index, you can modify the index or the query to ensure its application.