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.