What is the average year_max - year_min in these sql tables? - mysql

Question

I have 3 tables: actors, movies and cast:
mysql> desc actors;
+-----------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-----------+--------------+------+-----+---------+-------+
| id | int | NO | PRI | 0 | |
| full_name | varchar(200) | YES | | NULL | |
| gender | varchar(1) | YES | | NULL | |
+-----------+--------------+------+-----+---------+-------+
mysql> desc movies;
+-------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| id | int | NO | PRI | 0 | |
| title | varchar(100) | YES | | NULL | |
| year | int | YES | | NULL | |
| genre | varchar(100) | YES | | NULL | |
+-------+--------------+------+-----+---------+-------+
and
mysql> desc cast;
+----------+------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+------+------+-----+---------+-------+
| actor_id | int | YES | MUL | NULL | |
| movie_id | int | YES | MUL | NULL | |
| salary | int | YES | | NULL | |
+----------+------+------+-----+---------+-------+
The connection between tables is: cast.movie_id = movies.id and actors.id = cast.actor_id
The question: what is the average career longevity(years between the first film and the last film) of
actors who were at least in five films during their career?
I have tried to list actors ordered by the number of films, they took part in:
mysql> select full_name, count(title) as movie_title from cast, actors, movies
-> where cast.movie_id = movies.id and actors.id = cast.actor_id
-> group by full_name
-> order by movie_title
-> desc limit 2;
+--------------------------+-------------+
| full_name | movie_title |
+--------------------------+-------------+
| Kevin Bacon | 9 |
| Bill Paxton | 3 |
...
If what I've done is correct (not sure), we have only one such actor, so the question will be how to find this span
Will be very grateful for any advice!

Answer 1

How about:
SELECT AVG(YearsActive) TotalAverage
FROM (
-- by actor
SELECT a.id AS ActorId,
-- GROUP_CONCAT(a.full_name) AS ActorName,
(MAX(m.year) - MIN(m.year)) AS YearsActive
FROM actors a
INNER JOIN cast c ON a.id = c.actor_id
INNER JOIN movies m ON c.movie_id = m.id
GROUP BY a.id
HAVING COUNT(0) >= 5
) B
;