MySQL

**Verdict:** This skill is a strong, production-oriented MySQL reference that helps generate safer, more correct, and more performant queries than generic SQL knowledge alone. It emphasizes MySQL-specific behavior (InnoDB locking, utf8mb4/collations, replication modes, sql_mode strictness) and is particularly valuable when reliability and performance in real systems matter. **Strengths** - Covers critical MySQL quirks that commonly cause bugs or outages: character sets and collations, index limitations, isolation/locking behavior, non-transactional DDL, and replication edge cases. - Provides clear best practices (InnoDB-only for app data, consistent collations across tables, deadlock retry logic, avoiding query cache reliance, proper buffer pool sizing). - Includes version-aware notes (MySQL 8 features like expression indexes, FOR UPDATE SKIP LOCKED, EXPLAIN ANALYZE, and removal of query cache) that help avoid incorrect assumptions. - Useful not just for writing queries, but also for schema design, operations, and performance tuning. **Risks / Limitations** - MySQL-specific: not suitable for non-MySQL databases, and PostgreSQL habits can still leak through if not carefully checked. - Version sensitivity: guidance is tied to specific MySQL versions; users must still verify behavior against their exact server version and configuration. - Operational advice (e.g., changing innodb_buffer_pool_size, using pt-online-schema-change) assumes some DBA/ops competence; misapplication could still cause disruption. **Recommended Scenarios** - Generating or reviewing queries for production MySQL systems, especially where locking, replication, or strict GROUP BY behavior matters. - Assisting schema and index design for utf8mb4-heavy applications (e.g., emoji, multilingual text) and large text columns. - Supporting engineers migrating from PostgreSQL to MySQL who need to unlearn Postgres-specific assumptions (partial indexes, RETURNING, READ COMMITTED default, transactional DDL). - Providing guardrails for applications using MySQL 5.7+ or 8.x in environments where deadlocks, slow queries, or collation issues have caused historical problems.