mysql使用rand()进行随机查询
代码如下1 order by rand() limit x
随机mysql查询效率极其低下,今晚本人就遇到几个wordpress插件的作者,随机取值,竟然都是直接
代码如下 1 order by rand()
这也太坑爹了,数据一多,譬如你有个5万~10万,加上每天几千IP,那效率就跟蜗牛似的。不信你试试。这是严重不
负责任的随机查询。
后来百度找了一个方法
代码如下SELECT *
FROM table
WHERE id >= (
SELECT CEIL( RAND( ) * (
SELECT MAX( id )
FROM table ) ) )
LIMIT 1
或者
SELECT *
FROM table
WHERE id >= (
SELECT ROUND( RAND( ) * (
SELECT MAX( id )
FROM table ) ) )
LIMIT 1
但是还是没有效果了,再看下面
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 1
这样就快了很多哦,但是这个方法,会导致大部分的取值都在1/2前范围内,需要重新改造下:
代码如下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;
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