我得到了快速查询(大约0.5秒)，cpu很慢，在一个400K寄存器的MySQL数据库中随机选择10行，非缓存2Gb大小。在MySQL中快速选择随机行

$time= microtime_float();

$sql='SELECT COUNT(*) FROM pages';
$rquery= BD_Ejecutar($sql);
list($num_records)=mysql_fetch_row($rquery);
mysql_free_result($rquery);

$sql="SELECT id FROM pages WHERE RAND()*$num_records<20
   ORDER BY RAND() LIMIT 0,10";
$rquery= BD_Ejecutar($sql);
while(list($id)=mysql_fetch_row($rquery)){
    if($id_in) $id_in.=",$id";
    else $id_in="$id";
}
mysql_free_result($rquery);

$sql="SELECT id,url FROM pages WHERE id IN($id_in)";
$rquery= BD_Ejecutar($sql);
while(list($id,$url)=mysql_fetch_row($rquery)){
    logger("$id, $url",1);
}
mysql_free_result($rquery);

$time= microtime_float()-$time;

logger("num_records=$num_records",1);
logger("$id_in",1);
logger("Time elapsed: <b>$time segundos</b>",1);

SELECT column FROM table
ORDER BY RAND()
LIMIT 10

这不是有效的解决方案，但确实有效

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

SELECT
  * 
FROM
  table_with_600k_rows
WHERE
  RAND( ) 
ORDER BY
  id DESC 
LIMIT 30;

Id是主键，按Id排序， 解释table_with_600k_rows，发现该行不扫描整个表

我使用了Riedsio发布的http://jan.kneschke.de/projects/mysql/order-by-rand/(我使用了返回一个或多个随机值的存储过程的情况):

   DROP TEMPORARY TABLE IF EXISTS rands;
   CREATE TEMPORARY TABLE rands ( rand_id INT );

    loop_me: LOOP
        IF cnt < 1 THEN
          LEAVE loop_me;
        END IF;

        INSERT INTO rands
           SELECT r1.id
             FROM random AS r1 JOIN
                  (SELECT (RAND() *
                                (SELECT MAX(id)
                                   FROM random)) AS id)
                   AS r2
            WHERE r1.id >= r2.id
            ORDER BY r1.id ASC
            LIMIT 1;

        SET cnt = cnt - 1;
      END LOOP loop_me;

在这篇文章中，他通过维护一个表(使用触发器等)解决了id中的间隙导致不那么随机的结果的问题。参见文章); 我通过向表中添加另一列来解决这个问题，用连续的数字填充，从1开始(编辑:此列添加到运行时由子查询创建的临时表中，不影响永久表):

   DROP TEMPORARY TABLE IF EXISTS rands;
   CREATE TEMPORARY TABLE rands ( rand_id INT );

    loop_me: LOOP
        IF cnt < 1 THEN
          LEAVE loop_me;
        END IF;

        SET @no_gaps_id := 0;

        INSERT INTO rands
           SELECT r1.id
             FROM (SELECT id, @no_gaps_id := @no_gaps_id + 1 AS no_gaps_id FROM random) AS r1 JOIN
                  (SELECT (RAND() *
                                (SELECT COUNT(*)
                                   FROM random)) AS id)
                   AS r2
            WHERE r1.no_gaps_id >= r2.id
            ORDER BY r1.no_gaps_id ASC
            LIMIT 1;

        SET cnt = cnt - 1;
      END LOOP loop_me;

在文章中，我可以看到他花了很大的精力来优化代码;我不知道我的改变是否/有多大影响性能，但对我来说非常好。

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;