如果你想要一个随机记录(不管id之间是否有空隙):

PREPARE stmt FROM 'SELECT * FROM `table_name` LIMIT 1 OFFSET ?';
SET @count = (SELECT
        FLOOR(RAND() * COUNT(*))
    FROM `table_name`);

EXECUTE stmt USING @count;

来源:https://www.warpconduit.net/2011/03/23/selecting-a-random-record-using-mysql-benchmark-results/评论- 1266

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;

如果你只有一个读请求

将@redsio的答案与一个临时表结合起来(600K并不是很多):

DROP TEMPORARY TABLE IF EXISTS tmp_randorder;
CREATE TABLE tmp_randorder (id int(11) not null auto_increment primary key, data_id int(11));
INSERT INTO tmp_randorder (data_id) select id from datatable;

然后用一个@redsios的版本回答:

SELECT dt.*
FROM
       (SELECT (RAND() *
                     (SELECT MAX(id)
                        FROM tmp_randorder)) AS id)
        AS rnd
 INNER JOIN tmp_randorder rndo on rndo.id between rnd.id - 10 and rnd.id + 10
 INNER JOIN datatable AS dt on dt.id = rndo.data_id
 ORDER BY abs(rndo.id - rnd.id)
 LIMIT 1;

如果表比较大，可以先筛选第一部分:

INSERT INTO tmp_randorder (data_id) select id from datatable where rand() < 0.01;

如果你有很多读请求

Version: You could keep the table tmp_randorder persistent, call it datatable_idlist. Recreate that table in certain intervals (day, hour), since it also will get holes. If your table gets really big, you could also refill holes select l.data_id as whole from datatable_idlist l left join datatable dt on dt.id = l.data_id where dt.id is null; Version: Give your Dataset a random_sortorder column either directly in datatable or in a persistent extra table datatable_sortorder. Index that column. Generate a Random-Value in your Application (I'll call it $rand). select l.* from datatable l order by abs(random_sortorder - $rand) desc limit 1;

这个解决方案用最高和最低的random_sortorder来区分“边缘行”，所以在间隔中重新排列它们(一天一次)。

如果你想要一个随机记录(不管id之间是否有空隙):

PREPARE stmt FROM 'SELECT * FROM `table_name` LIMIT 1 OFFSET ?';
SET @count = (SELECT
        FLOOR(RAND() * COUNT(*))
    FROM `table_name`);

EXECUTE stmt USING @count;

来源:https://www.warpconduit.net/2011/03/23/selecting-a-random-record-using-mysql-benchmark-results/评论- 1266

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。

您可以轻松地使用带限制的随机偏移量

PREPARE stm from 'select * from table limit 10 offset ?';
SET @total = (select count(*) from table);
SET @_offset = FLOOR(RAND() * @total);
EXECUTE stm using @_offset;

您还可以像这样应用where子句

PREPARE stm from 'select * from table where available=true limit 10 offset ?';
SET @total = (select count(*) from table where available=true);
SET @_offset = FLOOR(RAND() * @total);
EXECUTE stm using @_offset;

在600,000行(700MB)表查询执行上的测试花费了大约0.016秒的硬盘驱动器时间。

EDIT:偏移量可能取接近表末尾的值，这将导致select语句返回更少的行(或者可能只有一行)，为了避免这种情况，我们可以在声明偏移量后再次检查，如下所示

SET @rows_count = 10;
PREPARE stm from "select * from table where available=true limit ? offset ?";
SET @total = (select count(*) from table where available=true);
SET @_offset = FLOOR(RAND() * @total);
SET @_offset = (SELECT IF(@total-@_offset<@rows_count,@_offset-@rows_count,@_offset));
SET @_offset = (SELECT IF(@_offset<0,0,@_offset));
EXECUTE stm using @rows_count,@_offset;