CREATE FAQS

1. How do I create a comment in Oracle?

To create a comment in Oracle, you use the COMMENT ON statement with the object type and name, followed by the comment text. The syntax is:

COMMENT ON <object_type> <object_name> IS 'comment_text';

For example, to add a comment on a table:

COMMENT ON TABLE employees IS 'This table stores employee details including personal information and job title.';

2. Can I create comments for all types of objects in Oracle?

Yes, you can create comments for various database objects, including tables, columns, views, indexes, sequences, and synonyms. Each object type has its own specific syntax but follows the same general structure for creating comments.

3. What is the maximum length of a comment in Oracle?

Oracle allows comments to be up to 4000 characters long. If you need more space for documentation, you may want to use external documentation systems.

4. Can comments affect the performance of the database?

No, comments in Oracle do not affect the performance or behavior of the database. They are purely for documentation purposes and stored in the data dictionary. The addition of comments does not slow down queries or operations.

5. How do I view comments in Oracle?

You can view existing comments using the following 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';

6. Can I update a comment in Oracle?

You cannot directly update a comment in Oracle. To modify a comment, you must first remove the existing comment by setting it to NULL and then re-add the new comment. For example:

1.     Remove the comment:

2.  COMMENT ON TABLE employees IS NULL;

3.     Add a new comment:

4.  COMMENT ON TABLE employees IS 'Updated description for the employee table.';

7. How do I delete a comment in Oracle?

To delete a comment, you use the COMMENT ON statement with IS NULL:

COMMENT ON <object_type> <object_name> IS NULL;

For example, to delete a comment from a table:

COMMENT ON TABLE employees IS NULL;

8. Can I create a comment for a column in a table?

Yes, you can create a comment for a column in a table. For example:

COMMENT ON COLUMN employees.salary IS 'This column stores the salary of employees.';

9. Are comments in Oracle visible to all users?

Comments are visible to users who have access to the specific object (e.g., a table or column). If a user has the necessary privileges to access a table, they will be able to see the comment associated with that table.

10. 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 delete the comment before dropping the object.

11. Can I create comments for system objects in Oracle?

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

12. Can I use comments for non-database objects?

Oracle comments are intended for database objects. If you need documentation for non-database objects (like code, PL/SQL procedures), you should use external documentation tools or comments in the code itself.

13. How can I automate the creation of comments for multiple objects?

You can write a script that uses dynamic SQL or PL/SQL to automate the creation of comments for multiple objects. For example:

BEGIN

  EXECUTE IMMEDIATE 'COMMENT ON TABLE employees IS ''This table stores employee details.''';

  EXECUTE IMMEDIATE 'COMMENT ON COLUMN employees.salary IS ''This column stores salary.''';

END;