DELETE FAQS

1. How do I delete a comment in Oracle?

To delete a comment on an object in Oracle, you use the COMMENT ON statement with IS NULL. The syntax is:

COMMENT ON <object_type> <object_name> IS NULL;

For example:

·        To remove a comment from a table:

·        COMMENT ON TABLE employees IS NULL;

·        To remove a comment from a column:

·        COMMENT ON COLUMN employees.salary IS NULL;

2. Does deleting a comment affect the database object?

No, deleting a comment does not affect the functionality or data of the object. It only removes the descriptive text or note associated with the object and has no impact on its structure or performance.

3. Can I delete comments for multiple objects at once?

No, you cannot delete comments for multiple objects in a single command. You need to issue separate COMMENT ON statements for each object whose comment you wish to remove.

4. How can I view the current comments before deleting them?

To view existing comments on objects like tables, columns, views, or indexes, you can query Oracle's data dictionary views:

·        For tables:

·        SELECT table_name, comments

·        FROM user_tab_comments

·        WHERE table_name = 'YOUR_TABLE_NAME';

·        For columns:

·        SELECT table_name, column_name, comments

·        FROM user_col_comments

·        WHERE table_name = 'YOUR_TABLE_NAME';

·        For views:

·        SELECT view_name, comments

·        FROM user_view_comments

·        WHERE view_name = 'YOUR_VIEW_NAME';

5. Can I undo the deletion of a comment?

Once a comment is deleted (set to NULL), there is no direct way to undo the action. You would need to manually re-add the comment using the COMMENT ON statement again.

6. What happens if I drop an object with a comment?

If you drop an object (such as a table, column, or index) that has a comment, the comment is automatically deleted along with the object. You do not need to manually remove the comment before dropping the object.

7. Can I use a script to delete comments for multiple objects?

Yes, you can use a script to delete comments for multiple objects. For example, a PL/SQL script could loop through the objects and delete their comments:

BEGIN

  EXECUTE IMMEDIATE 'COMMENT ON TABLE employees IS NULL';

  EXECUTE IMMEDIATE 'COMMENT ON COLUMN employees.salary IS NULL';

END;

8. Is there a limit to the size of a comment in Oracle?

Oracle allows comments to be up to 4000 characters in length. This is typically sufficient for most descriptions and notes, but it is something to keep in mind when managing large comments.

9. Can I delete comments for system objects?

No, you cannot delete comments on system objects (e.g., objects in the SYS schema). You can only delete comments for user-defined objects that you own or have permissions on.

10. Does deleting a comment impact other users or systems?

No, deleting a comment will not affect other users or systems directly. It only affects the documentation and descriptions associated with the object. If other users rely on the comment for context, they may lose that information.

11. How do I remove comments from a specific index or view?

To remove a comment from an index or view, you follow the same syntax as for tables or columns. For example:

·        To remove a comment from an index:

·        COMMENT ON INDEX idx_employee IS NULL;

·        To remove a comment from a view:

·        COMMENT ON VIEW employee_view IS NULL;

12. Can I remove a comment for a column in a table?

Yes, you can remove a comment from a column in a table using the following command:

COMMENT ON COLUMN employees.salary IS NULL;

13. What if I delete a comment that is important for documentation?

If you delete a comment that was important for documentation, you can always re-add it later using the COMMENT ON statement with the appropriate text.