DROP FAQS

1. What is the purpose of dropping comments in Oracle?

Dropping comments (notes) in Oracle allows you to remove descriptions or documentation associated with schema objects such as tables, columns, views, indexes, and sequences. This can be useful if the comment is outdated, irrelevant, or needs to be replaced with a new description.

2. How do I drop a comment from a table in Oracle?

To drop (remove) a comment from a table, use the following syntax:

COMMENT ON TABLE table_name IS NULL;

Example:

COMMENT ON TABLE employees IS NULL;

This will remove the comment associated with the employees table.

3. How do I drop a comment from a column in Oracle?

To remove a comment from a column within a table, you can use:

COMMENT ON COLUMN table_name.column_name IS NULL;

Example:

COMMENT ON COLUMN employees.salary IS NULL;

This removes the comment from the salary column of the employees table.

4. Can I drop comments from views or indexes in Oracle?

Yes, you can drop comments from views and indexes using the same method:

·        To drop a comment from a view:

·        COMMENT ON VIEW view_name IS NULL;

·        To drop a comment from an index:

·        COMMENT ON INDEX index_name IS NULL;

5. Can I drop a comment from a sequence in Oracle?

Yes, you can drop a comment from a sequence using the following syntax:

COMMENT ON SEQUENCE sequence_name IS NULL;

Example:

COMMENT ON SEQUENCE emp_id_seq IS NULL;

This removes the comment from the emp_id_seq sequence.

6. How do I view comments before dropping them?

Before dropping a comment, you can view it by querying the data dictionary views:

·        View comments on tables:

·        SELECT table_name, comments

·        FROM user_tab_comments

·        WHERE table_name = 'YOUR_TABLE_NAME';

·        View comments on columns:

·        SELECT table_name, column_name, comments

·        FROM user_col_comments

·        WHERE table_name = 'YOUR_TABLE_NAME';

7. Can I undo the action of dropping a comment in Oracle?

No, once a comment is dropped (set to NULL), the action is permanent and cannot be undone. If you need the comment back, you will have to re-add it manually using the COMMENT ON statement.

8. What happens if I drop a comment from a database object that is later dropped?

If you drop a database object (like a table, column, or index), its associated comment is also removed. However, the comment can be dropped explicitly with COMMENT ON <object_name> IS NULL even before the object is removed.

9. Does dropping a comment affect the functionality of the object in Oracle?

No, dropping a comment does not affect the functionality or data associated with the object. It simply removes the documentation or description that was provided for the object.

10. Can I track changes to comments in Oracle?

Oracle does not automatically track changes to comments. If you need to track changes to comments over time, you will need to implement an external auditing solution or manually document changes.

11. Can I drop comments on other database objects like constraints or triggers?

Oracle does not support dropping comments on triggers or constraints using the COMMENT ON statement directly. However, you can drop comments on tables, columns, views, indexes, and sequences.

12. What is the difference between DROP and COMMENT ON IS NULL?

The DROP command is used to remove entire database objects, such as tables, views, or sequences, from the schema. On the other hand, the COMMENT ON IS NULL command is used to remove the comment (note) associated with an object, but the object itself remains intact.

13. Is there a character limit for comments in Oracle?

Yes, Oracle allows comments to be up to 4000 characters in length, which should be sufficient for most descriptions. However, this limit applies to the length of a single comment.

14. Can I drop comments during object creation?

No, comments are typically added after creating an object. You can create the object using the CREATE statement, and then immediately drop or add comments using the COMMENT ON statement.

15. How do I drop comments on multiple objects at once?

Unfortunately, Oracle does not support a direct method to drop comments from multiple objects at once. You will need to use separate COMMENT ON IS NULL statements for each object whose comment you wish to remove.

16. Are comments dropped when an object is dropped?

Yes, when you drop an object such as a table, view, or index, its associated comments are also removed. However, you can drop the comment explicitly before dropping the object if you choose.