SQL script to convert from varchar to number without losing data

same time converting , in varchar to . for number column

alter table tablename add(dummycolumn number(20,2));

update tablename set dummycolumn = to_number(replace (actualcolumn,',','.'),'9999999999.99');

alter table tablename drop column actualcolumn cascade constraints;

alter table tablename rename column dummycolumn to actualcolumn;