The query rewrite component converts SQL statements that you enter into more efficient forms based on relational model equivalence. This shortens the period that the optimizer spends finding the optimal execution plan and greatly improves the execution efficiency of queries. Some common query transformations occur at this stage, such as subquery unnesting and predicate pushdown.
PolarDB for MySQL provides a wide range of query rewriting features that can be used in many scenarios and use cost-based optimization. Cost-based optimization allows PolarDB to determine the optimal query rewrite mode.
This following features specific to PolarDB for MySQL are detailed in subsequent topics: