The System Catalog - Database Systems - page 280

The Comment statement is the only SQL statement that allows direct update of
the system catalog by a user. It allows update of the Comments column in either the
Tab_Comments table or the Col_Comments table. The format of the command is:
Note : The column-name specified must be qualified by its table-name. The string
supplied is enclosed in single quotes.
In order to understand how this statement works, you need to familiarize
yourself with the structure and purpose of the catalog tables Tab_Comments and
Col_Comments . The Describe statement will allow you to view the structure (left as an
exercise). You will observe the following columns in respective tables:
The Tab_Comments table is used to store comments on tables of the database;
the Col_Comments table is used to store comments on table columns of the database.
The Comment statement allows modification of these comments.
Example 6: Store comments on tables and columns of the database:
To access these comments, you may query any of the following the views:
• DBA_Tab_Comments: All table comments for the database.
• USER_Tab_Comments: All table comments owned by the
current user.
• ALL_Tab_Comments: All table comments to which the current
user has access.
• DBA_Col_Comments: All column comments for the database.
• USER_Col_Comments: All column comments owned by the
current user.
• ALL_Col_Comments: All column comments to which the current
user has access.