MySQL从另一个表插入随机值

Question

嗨，我想从一个表中插入一些随机值到另一个表，我的查询看起来像这样：

INSERT INTO `rounds`(`matchID`, `questionOneID`, `questionTwoID`, `questionThreeID`) VALUES (17,(SELECT `id` FROM `questions` ORDER BY RAND() LIMIT 3))

问题是，mysql需要4个参数（matchID，questionOneID，...），并且仅获得两个参数（17，（...）），我如何告诉MySql它从SELECT获取3个参数？ 我真的必须：

INSERT INTO `rounds`(`matchID`, `questionOneID`, `questionTwoID`, `questionThreeID`) VALUES (17,(SELECT `id` FROM `questions` ORDER BY RAND() LIMIT 1),(SELECT `id` FROM `questions` ORDER BY RAND() LIMIT 1),(SELECT `id` FROM `questions` ORDER BY RAND() LIMIT 1))

或者，还有更好的方法？

Answer 1

您的查询看起来正确。 我会用insert . . . select编写它insert . . . select insert . . . select insert . . . select ：

INSERT INTO `rounds`(`matchID`, `questionOneID`, `questionTwoID`, `questionThreeID`)
     SELECT 17,
            (SELECT `id` FROM `questions` ORDER BY RAND() LIMIT 1),
            (SELECT `id` FROM `questions` ORDER BY RAND() LIMIT 1),
            (SELECT `id` FROM `questions` ORDER BY RAND() LIMIT 1);

如果您想保证这三个问题有所不同，那么我可以改用这种方法：

INSERT INTO `rounds`(`matchID`, `questionOneID`, `questionTwoID`, `questionThreeID`)
    SELECT 17,
           substring_index(group_concat(id order by rnd), ',', 1),
           substring(substring_index(group_concat(id order by rnd), ',', 2), ',', 11),
           substring_index(group_concat(id order by rnd), ',', -1),
    FROM (SELECT id, rand() as rnd FROM questions ORDER BY RAND() LIMIT 3) q

这会将三个随机问题放在一行上，没有重复项（除非id在questions重复）。