If the tables are small or if the frequency of queries that would make use of the functional index is small, then you may not benefit from creating a functional index.
如果表非常小，或者不经常执行使用函数索引的查询，那么创建函数索引可能收效甚微。
Running jobs at regular intervals is managed by the cron facility, which consists of the crond daemon and a set of tables describing what work is to be done and with what frequency.
以一定的时间间隔运行作业需要使用cron设施进行管理，它由crond守护进程和一组表(描述执行哪些操作和采用什么样的频率)组成。
By exploratory statistic analysis, the paper gave bivariate frequency contingency tables between every qualitative variable and every publishing company.
通过探索性统计分析，给出了调查报告中各定性变量和出版社间的二向频率列联表。
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