Oracle, Mysql ROW_NUMBER() OVER(...)

[Oracle] 

SELECT empno, ename, job, sal, 

            ROW_NUMBER() OVER(PARTITION BY job ORDER BY sal) AS rnum 

FROM scott.emp;

[MySQL]

SELECT empno, ename, job, sal, rnum

FROM (

   SELECT a.*, 

           (CASE @vjob WHEN a.job THEN @rownum:=@rownum+1 ELSE @rownum:=1 END) rnum,

           (@vjob:=a.job) vjob

   FROM emp a, (SELECT @vjob:='', @rownum:=0 FROM DUAL) b

   ORDER BY a.job, a.sal                  

) c;