What interesting things have you done with PostgreSQL/MySQL?

With PostgreSQL and MySQL, I often performed the following interesting tasks:

• Query optimization: analyzing execution plans, creating indexes, rewriting queries to improve performance.
• Replication and backups: setting up master-slave replication, automating data backup and recovery.
• Database schema migrations: using migration tools (e.g., Flyway, Liquibase) for safe schema updates.
• Configuring server parameters to enhance performance and stability.
• Working with triggers and stored procedures to implement business logic at the database level.
• Monitoring and diagnostics: using monitoring tools (pg_stat_statements, Percona Toolkit) to identify bottlenecks.

For example, in one project, I optimized a complex reporting query by adding a composite index and rewriting subqueries, which reduced execution time from minutes to seconds.