如果查询中的表极其小(通常少于1,000行)或者是群集表，而且查询根本没有选择性的话，那么使用表扫描会更好一些。
If the table in your query are pretty small (usually fewer than 1,000 rows) or clustered tables, and your query is not selective at all, it would be beneficial to use a table scan.
然而，如果每个不同的索引值都有许多重复的行，而所关联的表是高度群集的，那么通过索引添加的连接成本可能很低。
However, if there are many duplicate rows per distinct index value, and the associated table is highly clustered, the added costs of joining through the index can be slight.
对于一个具有 10行和三个群集的数据集，若使用电子数据表，需要花上30分钟才能完成。
With a data set of 10 rows and three clusters, that could take 30 minutes to work out using a spreadsheet.
如果您期望一个索引具有较高的群集因子，就只要重组该索引上的表。
If you expect an index to have a high cluster factor, just reorganize the table on that index.
如果使用电子数据表处理 100行数据和五个数据群集将会花费几个小时的计算时间，但WEKA在不到一秒钟的时间内就能给出答案。
Remember that 100 rows of data with five data clusters would likely take a few hours of computation with a spreadsheet, but WEKA can spit out the answer in less than a second.
如果表中的数据进行了群集化处理，或者是有物理次序的，那么表扫描的成本就可能相当低。
The costs of table scans can be fairly low if the data in the table is clustered or if it is in physical order.
尽可能避免表上有任何索引，尤其是不要有群集索引。
Avoid having any indexes on the table, if possible, but particularly not a clustering index.
对于索引控制的分区方法，分区的表、分区索引和群集这几个概念之间有点纠缠不清。
Under index-controlled partitioning, the concepts of partitioned table, partitioning index and clustering were all intertwined.
一个索引的群集程度；即，表中行的物理顺序与索引的符合程度。
The degree of clustering of an index; that is, the extent to which the physical sequence of rows in a table follows an index.
如果通常是顺序访问大量行(该表可能进行了群集)，那么比较大的页大小会更有效。
If typically more rows are accessed sequentially (maybe the table is clustered), then the larger page size is more efficient.
存在于表上的索引，包括它们索引的列，哪些是升序或降序的，以及哪些是群集的。
The indexes that exist on a table, including the columns that they index, whether they are ascending or descending, and whether they are clustered.
如果数据是群集的，它还可以提供更准确的统计信息(所获得的样本更好地代表了整个表数据)。
It may also provide more accurate statistics if the data is clustered (obtains a sample that better represents overall table data).
如果数据是群集的，它还可以提供更准确的统计信息(所获得的样本更好地代表了整个表数据)。
It may also provide more accurate statistics if the data is clustered (obtains a sample that better represents overall table data).
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