Most Frequent Co-Stars

A film archive stores casting credits in the film_credits table.

Table: film_credits

+--------------+---------+
| Column Name  | Type    |
+--------------+---------+
| film_id      | integer |
| actor_id     | integer |
| character_id | integer |
+--------------+---------+
+--------------+---------+
| Column Name  | Type    |
+--------------+---------+
| film_id      | integer |
| actor_id     | integer |
| character_id | integer |
+--------------+---------+

Each row records one character credit assigned to an actor in a film.

An actor may play multiple characters in the same film, so the same (film_id, actor_id) can appear more than once. Duplicate credit rows may also be present.

Find the actor pair or pairs that appeared together in the greatest number of films.

A pair counts once per film when both actors have at least one credit in that film, regardless of how many characters they played or how many duplicate credit rows exist.

Return only the pair or pairs whose collaboration_count equals the highest collaboration frequency. Include every tied pair.

Treat actor pairs as unordered and return them in canonical form with actor1 < actor2. Order the final result by actor1, then actor2.

If no film contains at least two distinct actors, return an empty result.

Output

+---------------------+---------+
| Column Name         | Type    |
+---------------------+---------+
| actor1              | integer |
| actor2              | integer |
| collaboration_count | integer |
+---------------------+---------+
+---------------------+---------+
| Column Name         | Type    |
+---------------------+---------+
| actor1              | integer |
| actor2              | integer |
| collaboration_count | integer |
+---------------------+---------+

Example

Input: film_credits

+---------+----------+--------------+
| film_id | actor_id | character_id |
+---------+----------+--------------+
| 101     | 10       | 1001         |
| 101     | 20       | 1002         |
| 101     | 30       | 1003         |
| 102     | 10       | 2001         |
| 102     | 20       | 2002         |
| 103     | 20       | 3001         |
| 103     | 30       | 3002         |
+---------+----------+--------------+
+---------+----------+--------------+
| film_id | actor_id | character_id |
+---------+----------+--------------+
| 101     | 10       | 1001         |
| 101     | 20       | 1002         |
| 101     | 30       | 1003         |
| 102     | 10       | 2001         |
| 102     | 20       | 2002         |
| 103     | 20       | 3001         |
| 103     | 30       | 3002         |
+---------+----------+--------------+

Output:

+--------+--------+---------------------+
| actor1 | actor2 | collaboration_count |
+--------+--------+---------------------+
| 10     | 20     | 2                   |
| 20     | 30     | 2                   |
+--------+--------+---------------------+
+--------+--------+---------------------+
| actor1 | actor2 | collaboration_count |
+--------+--------+---------------------+
| 10     | 20     | 2                   |
| 20     | 30     | 2                   |
+--------+--------+---------------------+

Explanation:

Film 101 contributes (10, 20), (10, 30), and (20, 30). Film 102 adds one collaboration for (10, 20), while film 103 adds one for (20, 30).

The maximum collaboration count is 2, so both tied pairs are returned.