该系列专题为2018年4月OCP-052考题变革后的最新题库。题库为小麦苗解答，若解答有不对之处，可留言，也可联系小麦苗进行修改。
Q题目
Which two are true about undo tablespaces?
A. Single-instance databases can have only one active undo tablespace.
B. They must have only one data file.
C. They can be recovered only when an instance is in MOUNT state.
D. They always retain undo for the time period defined by UNDO_RETENTION.
E. Tables can be created in undo tablespaces by SYS.
A答案
Answer：AC
对于B选项，Undo表空间可以包含多个数据文件。
对于D选项，只有当表空间设置为GUARANTEE时，才能确保已提交的数据保留UNDO_RETENTION参数设置的时间。
对于E选项，Undo表空间仅用于Undo段（在Undo表空间中不能创建其它段类型，例如表、索引等），只能与单个实例相关联。在任意指定时间，一个给定的实例只能有一个表空间是当前可写Undo表空间。
SYS@OCPASM1> CREATE TABLE TESTUNDO TABLESPACE UNDOTBS1 as select * from dual;
CREATE TABLE TESTUNDO TABLESPACE UNDOTBS1 as select * from dual
*
ERROR at line 1:
ORA-30022: Cannot create segments in undo tablespace
