查询语句语义优化的一个方法

查询语句语义优化的基本思想是,数据库所反映的现实世界的特定知识可以用来将查询语句变换成语义上等价但句法上不同的形式,以期寻找常规优化方法不可能找到的最优执行方案。本文提出了建立在费用模型及约束强度概念上的语义优化策略,并对查询语句中连接运算的删除作了进一步讨论。

A Strategy of Semantic Query Optimization

The principle idea of semantic query optimization is that specific knowledge about the real-world application which the database pertains to model,can be used to paraph- rase a given query in semantically equivalent yet syntactically different forms.The hope is that by introducing alternative statement of the orginal query,efficient imple- mentations may be discovered which would not have been considered by conventional query optimization alone.A strategy of semantic query optimization,which is based on cost model and the concept of constraint strength,is proposed.Further discussion on the deletion of join operations is given.