You can simply put line feeds inside the single-quotes of your comment declaration, for example:
COMMENT ON COLUMN MYTABLE.MYCOLUMN
IS
'Line 1
Line 2.
Line 3';
Note, however, that in SQL Developer (and perhaps other tools) this will not always display as expected. With the following query ...
SELECT *
FROM USER_COL_COMMENTS
WHERE
TABLE_NAME = 'MYTABLE'
AND COMMENTS IS NOT NULL;
... you'll get exactly what you're looking for in Script Output (i.e., highlight the query, right-click, select "Run Script"):
TABLE_NAME COLUMN_NAME COMMENTS
---------- ----------- --------------
MYTABLE MYCOLUMN Line 1
Line 2
Line 3
MYTABLE OTHERCOLUMN Other comments
But in a Query Result (i.e., highlight the query, right-click, select "Run Statement"), or when opening the table and looking at the Columns tab, the full comment will be run together on a single line.
Note: The tables in which these comments can be queried are:
- Comments on tables:
USER_TAB_COMMENTS
- Comments on columns:
USER_COL_COMMENTS