How to copy one column data into another column in oracle -

i want copy 1 column data column without replacing old data. example :

table-1

column1    column2   sony       sony  desc lenovo     lenovo desc  nokia      nokia desc  

i result

column 1        column2 sony            sony  desc sony  desc lenovo          lenovo desc  lenovo desc       nokia            nokia desc  nokia desc 

i have tried query not match

update table1 set column1 = column2 

if column1 has not null constraint, or if has primary key constraint, won't able insert null values. need filter out null values:

insert table1 (column1)   select column2     table1    column2 not null;