PHP Yii标准选择带限制的随机记录

Question

I have 1000 questions in the Question Model. How do I select 50 questions out of the 10000 randomly using Yii criteria ??

I am using Mysql as the Db

So far I have tried with the following

$criteria = new CDbCriteria;
$criteria->limit = 50;
$criteria->select = array('id');
$criteria->addCondition('chapter = xyz');

Answer 1

If you are using MySQL then it's:

$criteria->order = 'RAND()';

(updated from @topher answer)

Using this technique on a large number of rows will take a long time ( source ):

As soon as you have 10000 rows the overhead for sorting the rows becomes important.

In this case, refer to these answers:

• MySQL select 10 random rows from 600K rows fast
• How can i optimize MySQL's ORDER BY RAND() function?

Answer 2

The easiest solution: mysql's order by rand

$criteria->order('RAND()');

However from http://jan.kneschke.de/projects/mysql/order-by-rand/

As soon as you have 10000 rows the overhead for sorting the rows becomes important.

How to efficiently get random rows has been already been answered: MySQL select 10 random rows from 600K rows fast

Answer 3

$criteria->order(array('RAND()'));