I have a table with a structure like this: It has a lot of duplicates, I highlighted two duplicates so you can get an idea. So what I want to do is delete all duplicates and leave only one copy: as you can see it's a table with episodes from TV shows. How can I do this with an SQL command? So basically the command will look for rows with same show_id and same season and episodes and delete all the duplicates except one (There are episodes with 3 copies of the same episode).
THE SCREENSHOT : 
You can delete the duplicates by keeping all records except the one with the lowest id. In MySQL you can do this with a join on delete:
delete t
from <table> t left outer join
(select min(id) as minid
from <table t> t
group by show_id, season, episode
) tokeep
on t.id = tokeep.minid
where tokeep.minid is null;
Pretty simple solution of getting a list of ids (1 from each group) and deleting everything else from this question: How to delete duplicate rows with SQL?
DELETE FROM table WHERE id NOT IN
(SELECT MAX(id) FROM table GROUP BY show_id, season, episode);
You can also let MySql do the work for you adding UNIQE constraint using ALTER IGNORE TABLE ... syntax
ALTER TABLE Table1 ENGINE MyISAM; -- this obviously needed only if your ENGINE is not MyISAM
ALTER IGNORE TABLE Table1 ADD UNIQUE (`show_id`, `season`, `episode`);
ALTER TABLE Table1 ENGINE InnoDB; -- again this is only needed if your ENGINE was other than MyISAM
Here is SQLFiddle demo
