用于获取前3个rownum的子查询在pl / sql中不起作用

Question

DECLARE
    CURSOR EMPCUR 
      SELECT EMPNO,ENAME,SAL,ROWNUM 
        FROM (SELECT * 
                FROM EMP 
               ORDER BY SAL DESC) 
       WHERE ROWNUM<=3 
       ORDER BY ROWNUM;
BEGIN
  FOR EMPREC IN EMPCUR
  LOOP
    DBMS_OUTPUT.PUT_LINE('RANK '||EMPREC.ROWNUM);
    DBMS_OUTPUT.PUT_LINE(EMPREC.EMONO||' - '||EMPREC.ENAME||' - '||EMPREC.SAL);
  END LOOP;
END;
/

This code does not work:

ERROR at line 2: ORA-06550: line 2, column 17: PLS-00103: Encountered the symbol "SELECT" when expecting one of the following: ( ; is return The symbol "is" was substituted for "SELECT" to continue.

Answer 1

You have missed a IS on cursor declaration and there is a typo in line7 EMPREC.EMONO .

Try like this,

DECLARE
    CURSOR EMPCUR IS  SELECT EMPNO,ENAME,SAL,ROWNUM FROM (SELECT * FROM EMP ORDER BY SAL DESC) WHERE ROWNUM<=3 ORDER BY ROWNUM;
BEGIN
    FOR EMPREC IN EMPCUR
    LOOP
        DBMS_OUTPUT.PUT_LINE('RANK '||EMPREC.ROWNUM);
        DBMS_OUTPUT.PUT_LINE(EMPREC.EMPNO||' - '||EMPREC.ENAME||' - '||EMPREC.SAL);
    END LOOP;
END;
/

Answer 2

I would like to suggest that ranking things using the rownum pseudocolumn in a subquery is at best a flawed approach, rarely delivering on the actual goal. For instance, do you want the employees with the top three salaries? Or do you always want up to three records? How does this equation cope with employees with identical salaries? Et cetera.

It is a better approach to use the analytic functions, define your explicit rankings in those functions and return the results that actually answer the question.

begin
    for rec in ( select sq.*
                   from ( select e.employee_id
                               , e.first_name ||' '|| e.last_name as full_name 
                               , e.salary
                               , rank() over (order by e.salary desc) as salary_rank
                            from hr.employees e ) sq
                  where sq.salary_rank <= 3
                  order by sq.salary desc )
    loop
        dbms_output.put_line('RANK ' || rec.salary_rank);
        dbms_output.put_line(rec.employee_id || ' - ' || rec.full_name || ' - ' || rec.salary);
    end loop;
end;