MySQL 获取多条随机数据
一
select * from question order by rand() limit 10;问题：没有走索引，数据量大的时候非常慢
二
select * from question where id >= ((select max(id) from question) - (select min(id) from question)) * rand() + (select min(id) from question) limit 10;问题：随机行，如果数据分布不均匀会导致其筛出的数据集中在一侧
三
SELECT q.* FROM question q JOIN (SELECT question_id FROM question WHERE :your_where_condition AND rand() < ( SELECT (( $limit / count(*)) * 10 ) FROM question ) ORDER BY rand() LIMIT $limit) AS z ON z.question_id = q.question_id- 最终方案：在40w+数据的表中随机筛选10条数据0.3s左右，且数据分布较均匀，小ID也会被抽选到
- 在有主键索引的情况下，数据量300w+筛选10条数据花费的时间为2s
- 删除
rand() < ( SELECT (( $limit / count(*)) * 10 ) FROM question )条件后时间减少到了0.7s
