Un po' di calcolo potrebbe aiutare.
SQL> with test (col) as
2 (select date '2020-03-27' from dual union all
3 select date '2020-01-10' from dual union all
4 select date '2018-02-27' from dual union all
5 select date '2018-02-28' from dual
6 )
7 select col,
8 least(add_months(col, 1),
9 add_months(trunc(col, 'mm'), 1) + (col - trunc(col, 'mm'))
10 ) result
11 from test
12 order by col;
COL RESULT
---------- ----------
27.02.2018 27.03.2018
28.02.2018 28.03.2018
10.01.2020 10.02.2020
27.03.2020 27.04.2020
SQL>
