单项选择题

A.MERGEB.SELECT …CROSS JOINC.INSERT ALL …SELECTD.CREATE……

You are responsible for a data warehouse application that uses records from an external table to update one of the dimension tables periodically. The records in the external table may contain data for new rows in the dimension table， or for updates to its existing rows. Which type of SQL command would you use to transfer the data from the external table to the dimension table as efficiently as possible？（）

A.MERGE
B.SELECT …CROSS JOIN
C.INSERT ALL …SELECT
D.CREATE VIEW …CONSTRAINT

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