MySQL 如何高效率随机获取N条数据？

答案

假设表叫做mm_account。

ID连续的情况下（注意不能带where，否则结果不好）：

  1. SELECT *
  2. FROM `mm_account` AS t1 JOIN (SELECT ROUND(RAND() * (SELECT MAX(id) FROM `mm_account`)) AS id) AS t2
  3. WHERE t1.id >= t2.id
  4. ORDER BY t1.id ASC LIMIT 4;

ID不连续的情况下：

  1. SELECT * FROM `mm_account` 
  2. WHERE id >= (SELECT floor(RAND() * (SELECT MAX(id) FROM `mm_account`)))  and city="city_91" and showSex=1
  3. ORDER BY id LIMIT 4;

如果有一个字段叫id，最快的方法如下（随机获取5条）：

  1. SELECT * FROM mm_account 
  2. WHERE id >= ((SELECT MAX(id) FROM mm_account)-(SELECT MIN(id) FROM mm_account)) * RAND() + (SELECT MIN(id) FROM mm_account)
  3. limit 5;

如果带where语句，上面就不适合了，带where语句请看下面：

  1. SELECT *
  2. FROM `mm_account` AS t1 JOIN (SELECT ROUND(RAND() * (
  3. (SELECT MAX(id) FROM `mm_account` where id<1000 )-(SELECT MIN(id) FROM `mm_account` where id<1000 ))+(SELECT MIN(id) FROM `mm_account` where id<1000 )) AS id) AS t2
  4. WHERE t1.id >= t2.id
  5. ORDER BY t1.id LIMIT 5;

参考资料