использование
to_number(YourColumnName, FormatMask, NLS_NUMERIC_CHARACTERS = ',.') from ...
select to_number('12345.667677', '99999999D999999', 'NLS_NUMERIC_CHARACTERS = ''.,''')
from dual
select to_number('12345,667677', '99999999D999999', 'NLS_NUMERIC_CHARACTERS = '',.''')
from dual