SQL & PL/SQL

can you please give me the single decode statement for the below update statements -

update emp_company
set salary - 100
where ename = 'vijay';

update emp_company
set salary + 100
where ename = 'sunil';

I tired below but all the rows in the table are getting updated -

update emp_company
set salary = decode(ename,'vijay',salary-100,'sunil',salary+100);

Regards