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:
| Title | Description |
|---|---|
| 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 |
| Lateral Derived Optimization | Lateral Derived optimization, also referred to as "Split Grouping Optimization". |
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https://mariadb.com/kb/en/optimizations-for-derived-tables/