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Sales details are being stored on a daily basis in the SALES_2007 table. A large amount of data is added to the table daily. To save disk space，you issued the following command：   ALTER TABLE sales_2007 COMPRESS FOR ALL OPERATIONS；   What would be the outcome of this command？（）
A: It produces an error because data already exists in the table.
B: It produces an error because compression can be enabled at table creation only.
C: It compresses all data added or modified henceforth but the existing data in the table is not compressed immediately.
D: It immediately compresses all existing data as well as new data， resulting from either fresh additions or modifications to existing data.

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出自：Oracle认证

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