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1·The query optimizer does not recalculate the profile for tables automatically.

查询优化器不会自动重新计算表的配置文件。

2·However, if no indexes are available, the query optimizer must use a table scan.

但如果没有索引，则查询优化器必须扫描表。

3·The query optimizer will try to reduce the number of messages sent to the data source.

查询优化器将尝试减少发送到数据源的消息的数量。

4·The query optimizer is one of the most important components of a database system.

查询优化器是数据库系统最重要的组件之一。

5·STEP d: We need to explain the queries to view the access plans chosen by the DB2 query optimizer.

第4步：我们需要对查询进行explain(解释)，以查看DB 2查询优化器所选择的访问计划。

6·These views include columns containing statistical information that is useful to the query optimizer.

这些视图包括一些包含对查询优化器有用的统计信息的列。

7·The query optimizer bases query-cost estimates on the number of rows to be retrieved from each table.

查询优化器根据从每个表检索的行数估计查询成本。

8·Given accurate statistics, the query optimizer generally comes up with correct selectivity estimates.

如果有了准确的统计信息，那么查询优化器一般能够得出正确的选择性估计。

9·The output of the query optimizer on a federated system is the Federated Query Execution Plan (FQEP).

联邦系统上查询优化器的输出是联邦查询执行计划（Federated Query Execution Plan，FQEP）。

10·During plan generation for the query, the query optimizer communicates with the non-relational wrapper.

在为查询生成计划的过程中，查询优化器与非关系包装器通信。