Optimizations for Derived Tables
Derived tables are subqueries in the
FROM clause. Prior to MariaDB 5.3/MySQL 5.6, they were too slow to be usable. In MariaDB 5.3/MySQL 5.6, there are two
optimizations which provide adequate performance:
Condition Pushdown into Derived Table OptimizationIf a query uses a derived table (or a view), the first action that the que...
Derived Table Merge OptimizationMariaDB 5.3 introduced the derived table merge optimization
Derived Table with Key OptimizationSince MariaDB 5.3, the optimizer can create an index and use it for joins with other tables