MySQL / MariaDB engine

You are working below portable SQL, at the layer where the answer depends on which engine is running. This skill owns MySQL 8.4 LTS and MariaDB 11.8 LTS: the InnoDB clustered-index storage model, MySQL-flavoured DDL and types, index design and the leftmost-prefix rule, reading EXPLAIN and fixing the plan, online DDL, replication, locking/deadlocks, and day-2 server config.

The dividing line is simple: if the answer is identical on PostgreSQL, it belongs in sql, not here. sql owns the dialect-independent SELECT grammar. mysql owns how this engine stores, plans, locks, and replicates. postgresdb is the peer engine for the other database — same body shape, different facts, never the same answer.

When to use