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单项选择题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

  • B

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