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You just issued the following statement: ALTER TABLE SALES DROP COLUMN PROFIT. Which of the following choices identifies when the column will actually be removed from Oracle?（）
A:Immediately following statement execution 
B:After the ALTER TABLE DROP UNUSED COLUMNS command is issued 
C:After the ALTER TABLE SET UNUSED COLUMN command is issued 
D:After the ALTER TABLE MODIFY command is issued

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出自：Oracle认证

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