PHP Yii criteria select random records with limit

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');

score 5 · Accepted Answer · edited May 23 '17 at 12:33

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:

score 3 · Answer 2 · edited May 23 '17 at 12:01

3

The easiest solution: mysql's order by rand

$criteria->order('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

edited May 23 '17 at 12:01

Community

answered Apr 01 '14 at 09:47

topher

score 0 · Answer 3 · edited Jun 23 '15 at 07:30

0

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

edited Jun 23 '15 at 07:30

trejder

answered Apr 01 '14 at 09:47

Deepak Mane

It is important to point out, that [using `ORDER BY RAND()` is wrong](http://www.titov.net/2005/09/21/do-not-use-order-by-rand-or-how-to-get-random-rows-from-table/)! – trejder Jun 23 '15 at 07:30

3 Answers3