MySQL - 连接同一个表 4 次，其中第 2,3 和 4 列随机且全部不同

Question

为了简单起见，我们假设它只有 1 个字段。 ID。

在 MySQL 中，我想在结果的第一列中列出所有 ID 一次(按顺序)，但在第二、第三和第四列中，我想显示同一个表中的随机 ID - 所有 4 个 ID每行都需要不同。

我会直观地解释。例如 5 行表:

ID:

一个

B

C

D

E

结果应如下所示:

A B D C

公元前

CADB

D E C B

E A C B

我对 MySQL 很陌生——尽管在其他 SQL 方面有丰富的经验。我尝试使用 RAND() 和 LIMIT，但得到了不正确的结果 - 第 1 列有重复项，或者第 2,3 和 4 列始终只返回一个结果。

帮助 - 请

=)

Answer 1

MichaelRushton's method can optimize to
SELECT id1, id2, id3, id4 FROM (
SELECT t1.id id1, t2.id id2, t3.id id3, t4.id id4
FROM tt t1
    INNER JOIN tt t2 ON t2.id !=t1.id
    INNER JOIN tt t3 ON t3.id !=t1.id AND t3.id !=t2.id
    INNER JOIN tt t4 ON t4.id !=t1.id AND t4.id !=t2.id AND t4.id !=t3.id
ORDER BY RAND()) AS t
GROUP BY t.id1
ORDER BY NULL;

other method:
SELECT (@a:=`id`) AS a
 ,(@b:=(SELECT `id` FROM `tt` WHERE id NOT IN (@a) ORDER BY RAND() LIMIT 1)) AS b
 ,(@c:=(SELECT `id` FROM `tt` WHERE id NOT IN (@a,@b) ORDER BY RAND() LIMIT 1)) AS c
 ,(@d:=(SELECT `id` FROM `tt` WHERE id NOT IN (@a,@b,@c) ORDER BY RAND() LIMIT 1)) AS d
FROM `tt` AS t,(SELECT @a,@b,@c,@d) AS t2
ORDER BY t.id;

or

SELECT a, b, c,(SELECT `id` FROM `tt` AS td WHERE id NOT IN (a,b,c) ORDER BY RAND() LIMIT 1) AS d 
FROM (SELECT a, b,(SELECT `id` FROM `tt` AS tc WHERE id NOT IN (a,b) ORDER BY RAND() LIMIT 1) AS c 
    FROM (SELECT a,(SELECT `id` FROM `tt` AS tb WHERE id NOT IN (a) ORDER BY RAND() LIMIT 1) AS b 
        FROM (SELECT `id` AS a FROM `tt` AS ta) AS tt1
         ) AS tt2
      ) AS tt3
 ORDER BY a;

but its efficiency is very low!