RENAME

In Oracle, the RENAME statement is typically used to change the name of a database object like a table, column, index, or view. However, renaming comments (notes) associated with schema objects (such as tables, columns, views, etc.) is a bit different because there’s no specific RENAME COMMENT command.

Instead, to change or rename comments, you simply drop the old comment and add a new comment using the COMMENT ON statement.

Here’s a detailed explanation of how to rename comments or change comments for Oracle schema objects:

 

How to Rename Comments (Notes) in Oracle

Since there’s no direct RENAME command for comments, the typical approach to "renaming" a comment is:

1.     Drop the old comment (set the comment to NULL).

2.     Add a new comment (use the COMMENT ON statement with the updated description).

Syntax to Rename (Change) a Comment

To change a comment, the process involves two steps:

1.     Dropping the existing comment:

2.  COMMENT ON <object_type> <object_name> IS NULL;

3.     Adding a new comment:

4.  COMMENT ON <object_type> <object_name> IS 'Your new comment here';

·        <object_type>: The type of object (e.g., TABLE, COLUMN, VIEW, INDEX, etc.).

·        <object_name>: The name of the object (e.g., employees, salary, employee_view, etc.).

·        IS NULL: Removes the existing comment.

·        IS 'New comment text': Adds a new comment.

Examples of Renaming (Changing) Comments

1. Renaming a Comment on a Table

If you want to change the comment on the employees table, you would first remove the existing comment, then add a new one:

COMMENT ON TABLE employees IS NULL;  -- Remove the old comment

COMMENT ON TABLE employees IS 'This table stores detailed employee information, including department and job history.';  -- Add the new comment

2. Renaming a Comment on a Column

To change the comment on the salary column in the employees table:

COMMENT ON COLUMN employees.salary IS NULL;  -- Remove the old comment

COMMENT ON COLUMN employees.salary IS 'Employee salary, updated annually.';  -- Add the new comment

3. Renaming a Comment on a View

For a view (e.g., employee_view), you would perform the same steps:

COMMENT ON VIEW employee_view IS NULL;  -- Remove the old comment

COMMENT ON VIEW employee_view IS 'View that aggregates employee data for reporting purposes.';  -- Add the new comment

4. Renaming a Comment on an Index

If you want to change the comment on an index (e.g., idx_employee_name):

COMMENT ON INDEX idx_employee_name IS NULL;  -- Remove the old comment

COMMENT ON INDEX idx_employee_name IS 'Index created on employee name for faster lookups.';  -- Add the new comment

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How to View Comments Before Renaming Them

Before dropping a comment, you may want to view the existing comment for reference. You can do this 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';

·        View comments on views:

·        SELECT view_name, comments

·        FROM user_view_comments

·        WHERE view_name = 'YOUR_VIEW_NAME';

·        View comments on indexes:

·        SELECT index_name, comments

·        FROM user_index_comments

·        WHERE index_name = 'YOUR_INDEX_NAME';

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Important Notes on Renaming Comments

·        No direct RENAME for comments: Oracle does not support a direct RENAME COMMENT statement. To "rename" a comment, you must drop the existing comment and add a new one with the desired text.

·        NULL is used to drop comments: The method for removing a comment is setting it to NULL using the COMMENT ON statement.

·        Persistent: Once a comment is added, it remains in the data dictionary until it is explicitly removed or changed.

·        Tracking changes: Oracle does not natively track changes to comments, so you need an external solution (e.g., auditing) if you want to keep track of comment changes over time.