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 Optimization||If a query uses a derived table (or a view), the first action that the que...|
|Derived Table Merge Optimization||MariaDB 5.3 introduced the derived table merge optimization|
|Derived Table with Key Optimization||Since MariaDB 5.3, the optimizer can create an index and use it for joins with other tables|
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