MySQL: Group and flatten elements on a column

Question

If I have a view:

Movie             Genre    Actor
-------------------------------------------
Ocean's Twelve    Crime    George Clooney
Ocean's Twelve    Crime    Julia Roberts
Ocean's Twelve    Crime    Brad Pitt
Forrest Gump      Drama    Tom Hanks

How would I group by the movie title, but flatten the other columns like so:

Movie             Genre    Actor
-------------------------------------------
Ocean's Twelve    Crime    George Clooney, Julia Roberts, Brad Pitt
Forrest Gump      Drama    Tom Hanks

Note that if an element is equivalent, it is not repeated (e.g. Crime)

Answer 1

MySQL

Use GROUP_CONCAT() function:

SELECT movie, Genre, GROUP_CONCAT(Actor) AS Actor
FROM tableA
GROUP BY movie, Genre

SQL SERVER

SELECT A.movie, A.Genre, MAX(STUFF(B.ActorNames, 1, 1, '')) AS Actor
FROM tableA A 
CROSS APPLY(SELECT ' ' + Actor + ',' FROM tableA B 
            WHERE A.movie = B.movie AND A.Genre = B.Genre 
            FOR XML PATH('')
          ) AS B (ActorNames)
GROUP BY A.movie, A.Genre