How to mix SQL queries

There are at least two possibilities to solve this.

1. Using GROUP BY :

SELECT s.TITLE FROM series_episodes se
INNER JOIN series s ON se.SERIESID = s.ID
INNER JOIN series_trailers st ON se.ID = st.EPISODEID 
GROUP BY s.ID
ORDER BY se.ID DESC;

2. Using DISTINCT :

SELECT DISTINCT s.TITLE FROM series_episodes se
INNER JOIN series s ON se.SERIESID = s.ID
INNER JOIN series_trailers st ON se.ID = st.EPISODEID
ORDER BY se.ID DESC;

The result will always be the same.

Seeing the table series_trailers , it is quickly understood that you need to get the name of the author from it, creating a table dedicated solely to the authors. Otherwise, you will be forced to repeat a VARCHAR column several times. And if you also need to know that information for some reports, it will be much more complicated.

Let's see some tests and their results now.

SEE DEMO IN REXTESTER

Tables and data entered for the test

    CREATE TABLE IF NOT EXISTS series_trailers 
    (
        ID INT NOT NULL AUTO_INCREMENT PRIMARY KEY, 
        EPISODEID INT,
        CONTENT VARCHAR(255),
        AUTHORID INT

    )ENGINE=INNODB;

    INSERT INTO series_trailers (EPISODEID,CONTENT,AUTHORID)
        VALUES 
        (122383,'url1',  1),
        (9999,  'url2',  2),
        (923822,'stuff', 3),
        (122384,'url3',  4)
    ;

   /*Puede que el ID de esta tabla sea auto-incremental*/ 
   CREATE TABLE IF NOT EXISTS series_episodes 
    (
        ID INT NOT NULL PRIMARY KEY, 
        TITLE VARCHAR(255),
        SERIESID INT

    )ENGINE=INNODB;

    INSERT INTO series_episodes (ID,TITLE,SERIESID)
        VALUES 
        (122383,'Episode 1',23),
        (9999,  'Somethingweird',87),
        (923822,'Randomtitle',52),
        (122384,'Episode 2',23)
    ;


    /*Puede que el ID de esta tabla sea auto-incremental*/ 
    CREATE TABLE IF NOT EXISTS series 
    (
        ID INT NOT NULL PRIMARY KEY, 
        TITLE VARCHAR(255)

    )ENGINE=INNODB;    

    INSERT INTO series (ID, TITLE)
        VALUES 
        (23,'Stranger Things'),
        (87,'Seriesname'),
        (512,'Sometrashseries') 
    ;

   CREATE TABLE IF NOT EXISTS authors 
    (
        ID INT NOT NULL AUTO_INCREMENT PRIMARY KEY, 
        AUTHOR VARCHAR(255)

    )ENGINE=INNODB;  

    INSERT INTO authors (AUTHOR)
        VALUES 
        ('Peter'),
        ('Anna'), 
        ('Jhon'),
        ('Drake') ;

Test queries

   -- Con GROUP BY
SELECT s.TITLE FROM series_episodes se
INNER JOIN series s ON se.SERIESID = s.ID
INNER JOIN series_trailers st ON se.ID = st.EPISODEID 
GROUP BY s.ID
ORDER BY se.ID DESC;

  -- Con GROUP BY, incluyendo JOIN de AUTHORS
SELECT * FROM series_episodes se
INNER JOIN series s ON se.SERIESID = s.ID
INNER JOIN series_trailers st ON se.ID = st.EPISODEID 
INNER JOIN authors a ON a.ID=st.AUTHORID
GROUP BY s.ID
ORDER BY se.ID DESC;    

  -- Con DISTINCT
SELECT DISTINCT s.TITLE FROM series_episodes se
INNER JOIN series s ON se.SERIESID = s.ID
INNER JOIN series_trailers st ON se.ID = st.EPISODEID
ORDER BY se.ID DESC;

Results

-- Con GROUP BY

TITLE
Stranger Things
Seriesname

-- Con GROUP BY incluyendo JOIN de AUTHORS y todas las columnas

ID      TITLE           SERIESID    ID  TITLE               ID      EPISODEID   CONTENT     AUTHORID    ID  AUTHOR
122383  Episode 1       23          23  Stranger Things     1       122383      url1        1           1   Peter
9999    Somethingweird  87          87  Seriesname          2       9999        url2        2           2   Anna


-- Con DISTINCT

TITLE
Stranger Things
Seriesname

SELECT DISTINCT TITLE FROM series s LEFT JOIN series_episodies e ON s.id = e.seriesid LEFT JOIN series_trailer t on e.id = t.episodieid ORDER BY t.id DESC;

or you remove the distinct and you do a group by id, so what you do is to choose the title without repeating