how to convert a date string like this MM/YYYY to 01-MM-YY
SQL&gt; select to_char(to_date('03/1996', 'MM/YYYY'), 'DD-MON-YY') from dual;

TO_CHAR(T
---------
01-MAR-96


Based on that (if by convert you meant changing the data in the table):

update table tableX set columnX = to_char(to_date(columnX, 'MM/YYYY'), 'DD-MON-YY');