Have you worked with complex SQL queries or database optimization?

Yes, experience with complex SQL queries and database optimization often includes:

• Writing queries with multiple JOINs, subqueries, and aggregate functions.
• Using indexes to speed up data retrieval.
• Analyzing query execution plans (EXPLAIN) to identify bottlenecks.
• Optimizing queries by rewriting or adding indexes.
• Normalizing and denormalizing database schema depending on requirements.

For example, to speed up data retrieval, composite indexes are often created on columns involved in filters and sorting. It is also important to avoid redundant subqueries and use JOINs where they are effective.