多项选择题
Whichstatementsaretrueregardingtablecompression？（）
A.ItsavesdiskspaceandreducesmemoryusagE.
B.ItsavesdiskspacebuthasnoeffectonmemoryusagE.
C.ItincursextraCPUoverheadduringDMLaswellasdirectloadingoperations.
D.ItincursextraCPUoverheadduringDMLbutnotdirectloadingoperations.
E.ItrequiresuncompressoperationduringI/O.