【摘要】 对于一个给定的查询,通常会有多种不同的查询策略。查询优化就是从这些策略中找出最有效查询计划的一种过程。一个好的查询策略往往比一个坏的查询策略在执行效率(基于执行时间)上高几个数量级。简要说明了分布式数据库的特点,重点讨论了几种分布式查询策略的特点及其适用的情况。更多还原

【Abstract】 There are always many available solutions according to certain query task. Query optimization aim is to find the most efficient solution among many feasible query plans. An optimized query solution can often spend much little cost(based on executing time) than a worse one. The feature of distributed database is explained, it emphatically discusses many distributed query strategy and the applied ciucumstances.更多还原