Mysql RowNum

hi,
can any1 tell me wats wrong in the below query.It is showing as Fatal Error.
Select CriteriaName,criteriacode,ValueType,searchID, @rownum:=@rownum+1 as rownum
from criteria , (select @rownum := 1) as  r
where
productcode= 'compr' and @rownum=1
order by CriteriaName"
...