You could use a view:However, this has a great disadvantage: basic is a textual column, not numeric one, and you can no longer perform some operations (such as calculating sum) on it. The utility of this approach is therefore pretty limited.
Formatting is usually the responsibility of the client application. Database holds just the data, client applications (and SqlPlus is a client application in this context) format the data to display them to the user. Furthermore, the same column might be formatted differently in different contexts (eg. sometimes the full figure, sometimes just the thousands).
Client applications can look at database metadata to adapt their formatting to the data, if the information isn't used. If your column is declared as NUMBER(6,0), the client application can get this information and decide to display it using '999,999' format (there will be at most 6 digits in the number). If the column is declared NUMBER(5,3), a '90.000' format might be more appropriate. However, if all your columns are declared just as NUMBER, you're out of luck - it can contain anything from 0.000000000001 to 1000000000000000 (just making it up, the real range is even larger, of course). SqlPlus itself inspects the metadata to determine the width of textual columns, for example.