为了实现此目标，分区键应该在具有较高基数(换言之，即包含大量不同值)的列上选择。
To achieve this goal, the partitioning key should be selected on the columns that have high cardinality, or in other words, that contain a large number of distinct values.
基于优化器的估计，在目标索引键范围内有8个合格的RID。
Based on the optimizer's estimate, there are eight qualifying RIDs within the target index key range.
lookup将使用该键来为目标检索值。
The lookup will use the key to retrieve a value for the target.
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