053第256题

Posted 2020-09-19 yangykaifa

256.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.
Answer: C

You specify table compression with the COMPRESS clause of the CREATE TABLE statement. You can enable compression for an existing table by using these clauses in an ALTER TABLE statement. In this case, only data that is inserted or updated after compression is enabled is compressed. Similarly, you can disable table compression for an existing compressed table with the ALTER TABLE...NOCOMPRESS statement. In this case, all data that was already compressed remains compressed, and new data is inserted uncompressed.