pl / sql-to_date不与执行立即参数

exec procname(\'29-JAN-2011\');

PROCEDURE procname(pardate VARCHAR2) IS

  vardate DATE := to_date(pardate, \'DD-MON-YYYY\');
  SQLS VARCHAR2(4000);

BEGIN    

  SQLS := \'SELECT cola, colb
             FROM tablea 
            WHERE TRUNC(coldate) = TRUNC(TO_DATE(\'\'\'||pardate||\'\'\',\'\'DD/MON/YYYY\'\'))\';

  EXECUTE IMMEDIATE SQLS;

END;

EXEC procname(\'29-JAN-2011\');

PROCEDURE procname(pardate VARCHAR2) IS

  vardate DATE := to_date(pardate, \'DD-MON-YYYY\');
  SQLS VARCHAR2(4000)  := \'select cola, colb FROM tablea 
           WHERE TRUNC(coldate) = :1\';

   l_a tablea.cola%type;
   l_b tablea.colb%type;
BEGIN    
  EXECUTE IMMEDIATE SQLS 
      into l_a, l_b
      using vardate;
END;  

to_date