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Which three statements are true about dropping and unused columns in an Oracle database?spa
A) A primary key column referenced by another column as a foreign key can be dropped if using the CASCADE option.three
B) A DROP COLUMN command can be rolled backit
C) An UNUSED column's space is redaimed automatially when the block containing that column is next queriedio
D) An UNUSED column's space is redaimed automatially when the row containing that column is next queried.table
E) Partition key columns cannot be dropped.class
F) A column that is set to NNUSED still counts towards the limit of 1000 columns per table.sed
Answer:AEcommand
(解析:im
刪除主鍵列時能夠加 cascade 選項,同時把主外鍵約束一塊兒刪除。
ORA-12984: 沒法刪除分區列,E 對;