为了实现星型连接查询的最佳执行计划，优化器在适当的时候会考虑星型连接优化，并根据成本因素来决定星型连接计划。
The optimizer considers star join optimization when appropriate and decides on star join plan based on cost considerations in order to come up with best execution plan for a star join query.
当评估查询执行计划时，优化器计算并比较每种连接方法的成本，然后选择要使用的最佳方法。
The optimizer calculates and compares the costs of each join method and selects the best one to use when evaluating query execution plans.
更新统计数据是最重要的管理任务之一，它确保优化器选用最佳的查询执行计划。
Updating statistics is one of the most important administrative tasks that ensure the optimizer picks optimum execution plans for your queries.
统计视图和REOPT都使优化器可以计算出更精确的基数估计，而后选择一个最佳查询执行计划。
Both statistical views and REOPT allow the optimizer to compute a more accurate cardinality estimate and consequently choose an optimal query execution plan.
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.
DB 2 9.5优化器使用两种类型的索引来优化查询，并帮助选择最佳的查询执行计划。
The DB2 9.5 optimizer USES both type of indexes to optimize the queries and help selecting the best plan for query execution.
在前一个实例中，如果customer . customer_num和orders . customer_num都没有被索引，那么优化器将选择动态哈希连接来作为最佳的执行计划。
In the previous example, if customer.customer_num and orders.customer_num are not indexed, dynamic hash join would be chosen by the optimizer as the best execution plan.
一旦理解了自己的选择，就可以通过调整OPTCOMPIND参数，或者通过添加查询指示或索引，来影响优化器，从而选择最佳的查询执行计划。
Once you understand your options, you can influence the optimizer to select the best query execution plan, either by adjusting the OPTCOMPIND parameter or by adding query directives or indexes.
与Oracle和SQLServer等其他关系数据库管理系统一样，Informix也有内部优化器，负责选择最佳的查询执行计划。
Like other relational database management systems such as Oracle and SQL Server, Informix has its internal optimizer, which is responsible for selecting the best query execution plan.
与Oracle和SQLServer等其他关系数据库管理系统一样，Informix也有内部优化器，负责选择最佳的查询执行计划。
Like other relational database management systems such as Oracle and SQL Server, Informix has its internal optimizer, which is responsible for selecting the best query execution plan.
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