您可通过定义具有过滤条件的虚拟表，来有效地减少从源所读取记录的数量，并减小规则的总执行时间。

You can effectively reduce the number of records that are read from the source, and reduce the overall execution time of a rule, by defining a virtual table with a filter condition.

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还可以通过使用WHERE条件、ORDER BY、GROUP BY 子句执行过滤操作，或者执行常规基表适用的其他操作。

You can also perform operations such as filtering, using WHERE conditions, ORDER BY, GROUP BY, and other operations that would be possible with a regular base table.

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在某些条件下，会在merge语句执行过程中创建内部临时表，如清单7所示。

Under certain conditions, internal temporary tables are created during the execution of the merge statement, as shown in Listing 7.

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在某些条件下，会在merge语句执行过程中创建内部临时表，如清单7所示。

Under certain conditions, internal temporary tables are created during the execution of the merge statement, as shown in Listing 7.

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