If more than one column is aggregated using the same grouping key or without a grouping key, then all the aggregations are computed within the same operation with a single pass over the data.
如果利用相同的分组关键字或者没有分组关键字，来聚合多个列，那么，所有的聚合都在单个数据传递中的相同操作中进行。
Key operations in the control lifecycle are wrapped by a pair of events, one firing before the operation takes place and one firing immediately after the operation has completed.
控件生命周期中的关键操作被包装在一对事件中，一个在操作发生前触发，另一个在操作完成后立即触发。
If a key pair is successfully used in an encryption and decryption operation, the pair's private key must have been used for one part of the operation.
如果在加密和解密操作中成功地使用了密钥对，那么必定在操作的某个部分使用了密钥对中的私钥。
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