zoukankan      html  css  js  c++  java
  • mysql随机抽取数据

     
    --
    SELECT * FROM table_name ORDER BY rand() LIMIT 5;
    
    -- 较慢
    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;
    
    -- 快  `table 有 id 字段
    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;
    
    -- 快  `table 没有有 id 字段
    select * from (select @rownum:=@rownum + 1  as id,value from `table`,(select @rownum:=0) as a) as t1 join (
        select round( rand() * ( 
        (select max(b.id) from (select @rownum_max:=@rownum_max + 1  as id,value from `table`,(select @rownum_max:=0) as a) as b ) -
        (select min(b.id) from (select @rownum_min:=@rownum_min + 1  as id,value from `table`,(select @rownum_min:=0) as a) as b )
        )) + 
        (select min(b.id) from (select @rownum_min1:=@rownum_min1 + 1  as id,value from `table`,(select @rownum_min1:=0) as a) as b ) as id
    ) as t2
    on t1.id>= t2.id
    order by t1.id limit 1 

    缺点: 

    每次查询后会获得连续的n条数据

    解决办法:

    每次查一条数据,重复查询n 次

     
  • 相关阅读:
    播放m3u文件时不能时时更新的问题
    Oracle视图详解
    Oracle视图的作用与安全性
    Ext GridPanel 表头合并
    [AJAX] 001 AJAX核心操作
    [Java] 系统环境变量配置
    [AJAX] 002 AJAX异步验证
    判断文章/帖子操作权限
    让Tee 7.x版本和FastReport 3.x版本共存
    mysql基本语句
  • 原文地址:https://www.cnblogs.com/feiquan/p/12368131.html
Copyright © 2011-2022 走看看