For multiple index push-downs, multi-index scan is used to combine RIDs from different index scans, then skip-scan on the fact table is performed.
对于多索引下推，多索引扫描用于组合来自不同索引扫描的RID，然后就可以执行对事实表的跳跃式扫描了。
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Index push-downs require only a single-column index on the fact table, although they can use a multi-column index if the required foreign-key column is the first key in the index.