Choone two

Which three statements are true about dropping and unused columns in an Oracle database?

A) A primary key column referenced by another column as a foreign key can be dropped if using the CASCADE option.

B) A DROP COLUMN command can be rolled back

C) An UNUSED column's space is redaimed automatially when the block containing that column is next queried

D) An UNUSED column's space is redaimed automatially when the row containing that column is next queried.

E) Partition key columns cannot be dropped.

F) A column that is set to NNUSED still counts towards the limit of 1000 columns per table.

Answer：AE

(解析：

删除主键列时可以加 cascade 选项，同时把主外键约束一起删除。

ORA-12984: 无法删除分区列，E 对;