索引下推只需要事实表的单列索引，虽然在所需的外键列是索引的第一个键的情况下可以使用多列索引。
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.
利用下推连接技术的星型连接计划使得散列连接更加有效的主要原因是，在初期减少了事实表(探测表)的行数。
A star join plan utilizing push-down hash join technology makes hash joins more effective primarily due to reduction of fact table (probe table) rows early on.
如果只有几行从维度行中被选出，这样就只有几个键被下推，然后事实表的行数可能也会相应地减少。
If only a few rows are selected from the dimension table so that only a few keys are pushed down, then rows of the fact table might be reduced proportionally.
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。
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.
如这个查询计划所示，不止一个散列表的键可以被下推来过滤事实表的行。
As this query plan shows, keys from more than one hash table build can be pushed down to filter rows of the fact table.
在位向量下推中，对于每次下推，数据库服务器通过散列维度表中的键来创建发送至事实表的位向量。
In a bit-vector pushdown, for each push-down, the database server hashes the keys from the dimension table to create a bit vector, which is shipped to the fact table.
实际的比例取决于事实表中带有下推键的行的分布。
The actual proportion depends on the distribution of rows with the pushed-down keys in the fact table.
下推散列连接的主要目的是减少处理的事实表行数，这样可以探测每个散列表。
The primary purpose of a push-down hash join is to reduce number of rows processed from the fact table, which probes each of the hash tables.
星型连接计划中，数据库服务器在维度表中构建散列表的同时从维度表中下推键来过滤事实表。
In a star join plan, the database server pushes down keys from a dimension table to filter the fact table at the same time as it builds the hash table on the dimension table.
性能的提高取决于连接键被下推时所在维度表的过滤选择度。
The performance improvement depends on the selectivity of the filter on the dimension table from which the join keys are pushed down.
构建散列表时，连接键被下推用于过滤事实表的行，性能也显著提高。
When hash tables are built, join keys are pushed down and used to filter the rows of the fact table, and performance improves dramatically.
索引下推使用下推键执行事实表外键索引的查询。
An index pushdown USES the pushed-down keys to perform index lookups on a foreign key index of the fact table.
Location维度表中满足过滤条件的 location_id连接键被下推至Orders 表的索引。
The location_id join keys that meet the filter requirements on the Location dimension table are pushed down to the index on the Orders table.
Location维度表中满足过滤条件的 location_id连接键被下推至Orders 表的索引。
The location_id join keys that meet the filter requirements on the Location dimension table are pushed down to the index on the Orders table.
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