第 64 题 (多选题)： Which two statements are true about space-saving features in an Oracle Database.

A. An index created with the UNUSABLE attribute has no segment. B. Private Temporary Tables (PTTs) store metadata in memory only. C. Private Temporary Tables (PTTs) when used, are always dropped at the next commit statement. D. An index that is altered to be UNUSABLE will retain its segment. E. A table that is truncated will always have all of its extents removed 显示答案