SQL Query, Using Same Table Twice

Kaleb :

I'm trying to find the film list where two actors are together in a particular film. The correct query to use is the following

select f.title from film f
INNER JOIN film_actor fa1 ON f.film_id = fa1.film_id
INNER JOIN film_actor fa2 ON f.film_id = fa2.film_id
INNER JOIN actor a1 ON a1.actor_id = fa1.actor_id
INNER JOIN actor a2 ON a2.actor_id = fa2.actor_id
where 
(a1.first_name = 'CATE' and a1.last_name = 'MCQUEEN')
and
(a2.first_name = 'CUBA' and a2.last_name = 'BIRCH')

And the below method doesn't return any result:

select f.title from film f
INNER JOIN film_actor fa ON f.film_id = fa.film_id
INNER JOIN actor a1 ON a1.actor_id = fa.actor_id
INNER JOIN actor a2 ON a2.actor_id = fa.actor_id
where 
(a1.first_name = 'CATE' and a1.last_name = 'MCQUEEN')
and
(a2.first_name = 'CUBA' and a2.last_name = 'BIRCH')
;

Can someone help me understand why?

jeprubio :

In the second query by doing:

INNER JOIN actor a1 ON a1.actor_id = fa.actor_id
INNER JOIN actor a2 ON a2.actor_id = fa.actor_id

The actors a1 and a2 must be the same as they have the same id which is the value of fa.actor_id.

So, then, this actor should also have:

first_name = 'CATE' and last_name = 'MCQUEEN'
and
first_name = 'CUBA' and last_name = 'BIRCH'

at the same time. Which can't happen.

That's why you need to join it twice with film_actor table so that a1 and a2 can be different.