Database Software

How to use where condition to update only one particular row. For example, i've this table xmlsun3 which i created using the sample table employees in the HR schema

DECLARE
  l_xmltype XMLTYPE;
BEGIN
  SELECT sys_xmlagg(
           xmlelement(
             "EMP",
             xmlforest(e.employee_id, e.first_name,e.last_name,  e.job_id, e.manager_id, e.hire_date, e.salary, e.commission_pct)
           )
         )
  INTO   l_xmltype
  FROM   employees e;

  INSERT INTO xmlsun3 VALUES (l_xmltype);
  COMMIT;
END;
/

Now if i want to update salary of one particular row with first name as Steven, i tried the following statement

update xmlsun3 x
set value(x) =  updatexml(value(x),'/ROWSET/EMP/SALARY/text()','24500')
where extract(value(x),'/ROWSET/EMP/FIRST_NAME/text()').getStringVal() = 'Steven';

But it updates all the rows with the value 24500. I tried using existsnode, but the same result. How to update this one particular record?

Thanks,
Sundar