选择不在选定字段中的字段-MySQL

Question

我有一张桌子包含歌曲。我想选择3首最喜欢的歌曲和3首随机出现的歌曲，它们不在第一个查询中。

例如： 和预期的输出：

song 6, song 8, song 5 then *whatever song*,*whatever song*,*whatever song*

这是我尝试但无法使用的内容：

SELECT a.`song_id`, a.`name`, a.liked, b.song_id 
FROM `song` AS a, 
(SELECT song_id FROM song ORDER BY liked DESC LIMIT 3) as b 
WHERE a.song_id <> b.song_id LIMIT 3 

SELECT
    a.`song_id`, a.`name`, a.liked, b.ids
FROM
    `song` AS a,
    (SELECT substring_index(GROUP_CONCAT(DISTINCT song_id ORDER BY liked DESC SEPARATOR ','), ',', 3) as ids FROM song) as b
WHERE
    a.song_id not in(b.ids)

我正在使用MariaDB 10.1.29，它与子查询或LIMIT子句中的WITH不兼容。

Answer 1

在MariaDb 10.2和MySql 8.0中使用带有LIMIT的两个CTE's

第二个CTE随机执行，而没有从第一个CTE中选择

 WITH TOP3SONGS AS
 (
   SELECT *
   FROM song
   ORDER BY liked DESC
   LIMIT 3
 ),
 RANDOM3SONGS AS
 (
   SELECT *
   FROM song
   WHERE song_id NOT IN (select song_id from TOP3SONGS)
   ORDER BY rand()
   LIMIT 3
 )
 SELECT *
 FROM TOP3SONGS
 UNION ALL
 SELECT *
 FROM RANDOM3SONGS;

这在MySql 5.6中有效，因此很有可能也在MariaDb 10.1.29中
（我无法访问10.1，因此无法验证）

这次使用左连接到top3。
并按顺序将top3置于限制6之前的随机数之上。

SELECT song.*
FROM song
LEFT JOIN 
(  SELECT song_id, liked 
   FROM song 
   ORDER BY liked DESC 
   LIMIT 3
) top3songs ON top3songs.song_id = song.song_id
ORDER BY top3songs.liked DESC, RAND()
LIMIT 6;

对 db <>小提琴here

的测试

Answer 2

您应该将其拆分为两个，然后合并结果： 首先查询以选择前3个：

SELECT song_id FROM song ORDER BY liked DESC LIMIT 3

第二次查询选择随机三首，不包括上面选择的歌曲：

SELECT song_id FROM song WHERE song_id NOT IN (
   SELECT song_id FROM song ORDER BY liked DESC LIMIT 3
) ORDER BY RAND() LIMIT 3

现在在一起：

SELECT song_id FROM song ORDER BY liked DESC LIMIT 3
UNOION
SELECT song_id FROM song WHERE song_id NOT IN (
   SELECT song_id FROM song ORDER BY liked DESC LIMIT 3
) ORDER BY RAND() LIMIT 3

Answer 3

目前我只安装了MariaDB 10.3，但是我在较旧的MySQL 4.1上尝试了以下语法，并且都返回了相同的结果。

SELECT * FROM (
(SELECT * FROM song ORDER BY liked DESC LIMIT 3) UNION
(SELECT A.* FROM song A LEFT JOIN (SELECT * FROM song ORDER BY liked DESC LIMIT 3) B ON A.song_id=B.song_id 
WHERE B.song_id IS NULL ORDER BY RAND() LIMIT 3)) S ORDER BY liked DESC;