Oracle Database SQL — Question 192

Which three statements are true about dropping and unused columns in an Oracle database? (Choose three.)

Answer options

• A. An UNUSED column's space is reclaimed automatically when the row containing that column is next queried.
• B. A column that is set to UNUSED still counts towards the limit of 1000 columns per table.
• C. A DROP COLUMN command can be rolled back.
• D. A primary key column referenced by another column as a foreign key can be dropped if using the CASCADE option.
• E. An UNUSED column's space is reclaimed automatically when the block containing that column is next queried.
• F. Partition key columns cannot be dropped.

Correct answer: B, D, F

Explanation

Option B is correct because an UNUSED column does count towards the maximum limit of columns allowed in a table. Option D is also correct as it allows for the dropping of a primary key column if it is referenced as a foreign key when using the CASCADE option. Option F is correct as partition key columns are not permissible to drop, while the other options contain inaccuracies regarding how space is reclaimed and the rollback capability of the DROP COLUMN command.