key： key(确定您已经将键值标记为外部性标识符)。
Key: key (make sure that you mark the key as the external identifier).
像SSIS这样的ETL工具就可以实现这些功能，如，在不同的系统间进行数据的移动、数据的再格式化、完整性校验、关键值查询、衍生跟踪等，SSIS也证明了它是一个有能力和有着多方面用途的ETL工具。
ETL tools like SSIS can perform these functions such as moving data between systems, reformatting data, integrity checking, key lookups, tracking lineage, and more.
首先在逻辑上将表与其自身连接，然后将更具有选择性的非起始索引键作为索引绑定过滤器，应用于起始键值的每个惟一的组合。
The table is logically joined to itself, and the more selective non-leading index keys are applied as index bound filters to each unique combination of the leading key values.
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