MySQL - 获取列中的平均值

Question

I'm making a list with certain songs. Each song has its own unique ID. OK let's say I have this table called list. A new:

The ID is self-explanatory. It's used to ID rows. song_one through song_ten is filled with a song's unique ID.

Every time a user makes a new list, they add songs and each row gets filled. Now, how would I get the average rank of the songs in the tables list using the song's ID that is filled between song_one through song_ten?

Answer 1

Redesign your database. Make a new table with songid, listid and rank. This will make your job easy.

listsongs
-----------------
songid [PK] -- Foreign key referencing the songs table
listid [PK] -- Foreign key referencing the lists table
rank

Selecting average song ranks:

SELECT
    a.song_id
    AVG(b.rank) AS avgrank
FROM
    songs a
LEFT JOIN
    listsongs b PM a.song_id = b.song_id
GROUP BY
    a.song_id