mysql中RAND()随便查询记录效率问题和解决办法分享

复制代码 代码如下:

#auther: 小强(占卜师)
#date: 2008-03-31
create table randnumber
select -1 as number
union
select -2
union
select -3
union
select -4
union
select -5
union
select 0
union
select 1
union
select 2
union
select 3
union
select 4
union
select 5

#得到随机数
#auther: 小强(占卜师)
#date: 2008-03-31
select number
from randnumber order by rand() limit 1

复制代码 代码如下:

SELECT ROUND((0.5-RAND())*2*5)
#注释
#0.5-rand()可以得到-0.5 至 +0.5的随机数
#(0.5-rand())*2可以得到-1 至 +1的随机数
#(0.5-rand())*2*5可以得到-5 至 +5的随机数
#ROUND((0.5-RAND())*2*5)可以得到-5 至 +5的随机整数

复制代码 代码如下:

SELECT * FROM `table` AS t1 JOIN (SELECT ROUND(RAND() * (SELECT MAX(id) FROM `table`)) AS id) AS t2 WHERE t1.id >= t2.id ORDER BY t1.id ASC LIMIT 5;

复制代码 代码如下:

SELECT * FROM `table` WHERE id >= (SELECT FLOOR( MAX(id) * RAND()) FROM `table` ) ORDER BY id LIMIT 1;

复制代码 代码如下:

SELECT * FROM `table`
WHERE id >= (SELECT floor(RAND() * (SELECT MAX(id) FROM `table`)))
ORDER BY id LIMIT 1;

复制代码 代码如下:

SELECT * FROM `table`
WHERE id >= (SELECT floor( RAND() * ((SELECT MAX(id) FROM `table`)-(SELECT MIN(id) FROM `table`)) + (SELECT MIN(id) FROM `table`)))
ORDER BY id LIMIT 1;
SELECT *
FROM `table` AS t1 JOIN (SELECT ROUND(RAND() * ((SELECT MAX(id) FROM `table`)-(SELECT MIN(id) FROM `table`))+(SELECT MIN(id) FROM `table`)) AS id) AS t2
WHERE t1.id >= t2.id
ORDER BY t1.id LIMIT 1;