另一个简单的解决方案是对行进行排名，并随机获取其中之一，有了这个解决方案，你将不需要在表中有任何基于“Id”的列。

SELECT d.* FROM (
SELECT  t.*,  @rownum := @rownum + 1 AS rank
FROM mytable AS t,
    (SELECT @rownum := 0) AS r,
    (SELECT @cnt := (SELECT RAND() * (SELECT COUNT(*) FROM mytable))) AS n
) d WHERE rank >= @cnt LIMIT 10;

您可以根据需要更改限制值，以便访问尽可能多的行，但大多数情况下是连续的值。

然而，如果你不想要连续的随机值，那么你可以获取一个更大的样本并从中随机选择。就像……

SELECT * FROM (
SELECT d.* FROM (
    SELECT  c.*,  @rownum := @rownum + 1 AS rank
    FROM buildbrain.`commits` AS c,
        (SELECT @rownum := 0) AS r,
        (SELECT @cnt := (SELECT RAND() * (SELECT COUNT(*) FROM buildbrain.`commits`))) AS rnd
) d 
WHERE rank >= @cnt LIMIT 10000 
) t ORDER BY RAND() LIMIT 10;

一个伟大的职位处理几个情况，从简单，到差距，到不均匀与差距。

http://jan.kneschke.de/projects/mysql/order-by-rand/

对于大多数一般情况，你可以这样做:

SELECT name
  FROM random AS r1 JOIN
       (SELECT CEIL(RAND() *
                     (SELECT MAX(id)
                        FROM random)) AS id)
        AS r2
 WHERE r1.id >= r2.id
 ORDER BY r1.id ASC
 LIMIT 1

这假设id的分布是相等的，并且id列表中可能存在间隙。有关更高级的示例，请参阅本文

我认为这是一个简单但更快的方法，我在现场服务器上测试了它，与上面的几个答案相比，它更快。

 SELECT * FROM `table_name` WHERE id >= (SELECT FLOOR( MAX(id) * RAND()) FROM `table_name` ) ORDER BY id LIMIT 30; 

//对一个130行的表花费0.0014秒

SELECT * FROM `table_name` WHERE 1 ORDER BY RAND() LIMIT 30

//对130行的表花费0.0042秒

 SELECT name
FROM random AS r1 JOIN
   (SELECT CEIL(RAND() *
                 (SELECT MAX(id)
                    FROM random)) AS id)
    AS r2
WHERE r1.id >= r2.id
ORDER BY r1.id ASC
LIMIT 30

//对130行的表花费0.0040秒

所有最好的答案都已经贴出来了(主要是那些引用了http://jan.kneschke.de/projects/mysql/order-by-rand/的链接)。

I want to pinpoint another speed-up possibility - caching. Think of why you need to get random rows. Probably you want display some random post or random ad on a website. If you are getting 100 req/s, is it really needed that each visitor gets random rows? Usually it is completely fine to cache these X random rows for 1 second (or even 10 seconds). It doesn't matter if 100 unique visitors in the same 1 second get the same random posts, because the next second another 100 visitors will get different set of posts.

当使用这种缓存时，你也可以使用一些较慢的解决方案来获取随机数据，因为不管你的req/s如何，它每秒只会从MySQL中获取一次。

从书中:

使用偏移量选择随机行

这是另一种避免前面提到的问题的技术 替代方法是统计数据集中的行数并返回一个随机值 0到计数之间的数字。然后用这个数字作为抵消 查询数据集时

$rand = "SELECT ROUND(RAND() * (SELECT COUNT(*) FROM Bugs))";
$offset = $pdo->query($rand)->fetch(PDO::FETCH_ASSOC);
$sql = "SELECT * FROM Bugs LIMIT 1 OFFSET :offset";
$stmt = $pdo->prepare($sql);
$stmt->execute( $offset );
$rand_bug = $stmt->fetch();

在不能假定连续键值和时使用此解决方案 您需要确保每一行都有均等的机会被选中。

我改进了@Riedsio的答案。这是我在一个有间隙的大型均匀分布表上能找到的最有效的查询(测试从一个有> 2.6B行的表中获得1000个随机行)。

(SELECT id FROM table INNER JOIN (SELECT FLOOR(RAND() * @max := (SELECT MAX(id) FROM table)) + 1 as rand) r on id > rand LIMIT 1) UNION
(SELECT id FROM table INNER JOIN (SELECT FLOOR(RAND() * @max) + 1 as rand) r on id > rand LIMIT 1) UNION
(SELECT id FROM table INNER JOIN (SELECT FLOOR(RAND() * @max) + 1 as rand) r on id > rand LIMIT 1) UNION
(SELECT id FROM table INNER JOIN (SELECT FLOOR(RAND() * @max) + 1 as rand) r on id > rand LIMIT 1) UNION
(SELECT id FROM table INNER JOIN (SELECT FLOOR(RAND() * @max) + 1 as rand) r on id > rand LIMIT 1) UNION
(SELECT id FROM table INNER JOIN (SELECT FLOOR(RAND() * @max) + 1 as rand) r on id > rand LIMIT 1) UNION
(SELECT id FROM table INNER JOIN (SELECT FLOOR(RAND() * @max) + 1 as rand) r on id > rand LIMIT 1) UNION
(SELECT id FROM table INNER JOIN (SELECT FLOOR(RAND() * @max) + 1 as rand) r on id > rand LIMIT 1) UNION
(SELECT id FROM table INNER JOIN (SELECT FLOOR(RAND() * @max) + 1 as rand) r on id > rand LIMIT 1) UNION
(SELECT id FROM table INNER JOIN (SELECT FLOOR(RAND() * @max) + 1 as rand) r on id > rand LIMIT 1)

让我来解释一下发生了什么。

(SELECT MAX(id) FROM table) 我在计算并保存最大值。对于非常大的表，每次需要一行时计算MAX(id)都会有轻微的开销 SELECT FLOOR(rand() * @max) + 1 as rand) 获取一个随机id SELECT id FROM table INNER JOIN(… 这就填补了空白。基本上，如果你在间隙中随机选择一个数字，它就会选择下一个id。假设间隙是均匀分布的，这应该不是问题。

进行联合可以帮助您将所有内容放入一个查询中，从而避免进行多个查询。它还可以节省计算MAX(id)的开销。根据您的应用程序，这可能非常重要，也可能无关紧要。

注意，这只获取id，并以随机顺序获取它们。如果你想做更高级的事情，我建议你这样做:

SELECT t.id, t.name -- etc, etc
FROM table t
INNER JOIN (
    (SELECT id FROM table INNER JOIN (SELECT FLOOR(RAND() * @max := (SELECT MAX(id) FROM table)) + 1 as rand) r on id > rand LIMIT 1) UNION
    (SELECT id FROM table INNER JOIN (SELECT FLOOR(RAND() * @max) + 1 as rand) r on id > rand LIMIT 1) UNION
    (SELECT id FROM table INNER JOIN (SELECT FLOOR(RAND() * @max) + 1 as rand) r on id > rand LIMIT 1) UNION
    (SELECT id FROM table INNER JOIN (SELECT FLOOR(RAND() * @max) + 1 as rand) r on id > rand LIMIT 1) UNION
    (SELECT id FROM table INNER JOIN (SELECT FLOOR(RAND() * @max) + 1 as rand) r on id > rand LIMIT 1) UNION
    (SELECT id FROM table INNER JOIN (SELECT FLOOR(RAND() * @max) + 1 as rand) r on id > rand LIMIT 1) UNION
    (SELECT id FROM table INNER JOIN (SELECT FLOOR(RAND() * @max) + 1 as rand) r on id > rand LIMIT 1) UNION
    (SELECT id FROM table INNER JOIN (SELECT FLOOR(RAND() * @max) + 1 as rand) r on id > rand LIMIT 1) UNION
    (SELECT id FROM table INNER JOIN (SELECT FLOOR(RAND() * @max) + 1 as rand) r on id > rand LIMIT 1) UNION
    (SELECT id FROM table INNER JOIN (SELECT FLOOR(RAND() * @max) + 1 as rand) r on id > rand LIMIT 1)
) x ON x.id = t.id
ORDER BY t.id