ora-09004

ora-09004 invalid identifier

hello, i am having problem with my query... this one works.. select name, bday, address, dbms_random.value(1, 100) as joker from employee order by joker asc but when i try to get what i want using either the 'where' and group/having clause, i am having a ora-09004 (invalid identifier) ERROR.. e.g. select name, bday, addres...