1.1、查询优化和执行(Optimization and Execution) MySQL 将用户的查询语句进行解析,并创建一个内部的数据结构——分析树,然后进行各种优化,例如重写查询、选择读取表的顺序,以...
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要改进性能,联合需要经常使用缓存、物理查询表(MQT)以及分布式查询优化和执行。
To improve performance, federation frequently USES caching, materialized query tables (MQTs), and distributed query optimization and execution.
输入的每个SQL查询都必须被解析、优化和执行。
Every SQL query that is entered must be parsed, optimized and executed.
对于优化器不能选择最佳查询执行计划的例外情况,DB 2已经增加了诸如selectivity子句和优化指南之类的特性。
For the exceptional situations where the optimizer cannot choose an optimal query execution plan, DB2 has added features such as the SELECTIVITY clause and optimization guidelines.
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