Hi everyone!

i'm trying to build a query for a movie database (actually it's just an example from a book, but not a real database), that should show me all the movies that have a longer length than the average one.

So far i came till this query here:
select title
 from movie
 group by title
 having length > avg(length) ;
which for some reasons isn't right ...

I already searched a lot on the google. In most of the AVG queries at the having clause they compare the avg(length) with some scalar value, which in my case isn't worth doing. There must be some way for comparison of the avg(length) with the actual values of the length, right?
Can anyone please explain me what's wrong with my query, and how exactly should it look like ?

I don't know whether is makes any difference but I'm using Mysql 5.

here is also a small table i created in order to test my query.
create table movie
title varchar(20),
year date,
length numeric(4,2),
studioname varchar(20),
producernr int