在一些地方，你可以想借多少书就借多少，但在其他地方，你只限于借阅一定数量的书几个星期，这样你可以有足够的时间读完所有已借的书。
In some places, you may borrow as many books as you want, but in others you are limited to a certain number of books for several weeks so that you can have enough time to finish all the books you've borrowed.
对于结果的每一行，有一定数量的总是能够访问的属性，这些属性就变成了全局项目类。
On each result row is a certain number of properties that are always accessible, and these properties became the global item class.
如果表格有一定数量的片段键(或者分区键)值，而且在片段键上有同等谓词的表格上查询时，它会很有用处。
It is useful when a table has a finite set of values for the fragment key (or partitioning key) and queries on the table have an equality predicate on the fragment key.
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