blocks|key|748360|text|Thing.first(:order+=>+"RANDOM()")+#+For+MySQL+:order+=>+"RAND()",+-+thanx,+@DanSingerman
#+Rails+3
Thing.order("RANDOM()").first|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|748361|或|unstyled|748362|Thing.first(:offset+=>+rand(Thing.count))
#+Rails+3
Thing.offset(rand(Thing.count)).first|748363|实际上，在Rails3中，所有示例都可以工作。但是对于大表来说，使用order+RANDOM的速度很慢，但更像是sql风格的。|offset|length|style|CODE|748364|UPD。您可以对索引列使用以下技巧(PostgreSQL语法)：|748365|select+*+
from+my_table+
where+id+>=+trunc(
++random()+*+(select+max(id)+from+my_table)+%2B+1
)+
order+by+id+
limit+1;|748366|entityMap^0|0|0|0|14|6|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|V|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|W|8|@]|9|@]|A|$B|C]]|$1|I|3|J|5|F|7|X|8|@$K|Y|L|Z|M|N]]|9|@]|A|$]]|$1|O|3|P|5|F|7|10|8|@]|9|@]|A|$]]|$1|Q|3|R|5|6|7|11|8|@]|9|@]|A|$B|C]]|$1|S|3|-4|5|F|7|12|8|@]|9|@]|A|$]]]|T|$]]

<pre><code>Thing.first(:order =&gt; "RANDOM()") # For MySQL :order =&gt; "RAND()", - thanx, @DanSingerman
# Rails 3
Thing.order("RANDOM()").first
</code></pre>

or

<pre><code>Thing.first(:offset =&gt; rand(Thing.count))
# Rails 3
Thing.offset(rand(Thing.count)).first
</code></pre>

Actually, in Rails 3 all examples will work. But using order <code>RANDOM</code> is quite slow for big tables but more sql-style

UPD. You can use the following trick on an indexed column (PostgreSQL syntax):

<pre><code>select * 
from my_table 
where id &gt;= trunc(
 random() * (select max(id) from my_table) + 1
) 
order by id 
limit 1;
</code></pre>

blocks|key|964213|text|为此，我做了一个Rails3gem，它在大型表上执行得更好，并允许您链接关系和作用域：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|964214|https://github.com/spilliton/randumb|offset|length|964215|(编辑)：我的gem的默认行为基本上使用与上面相同的方法，但如果您愿意，您可以选择使用旧方法:)|964216|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|10|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@$D|Q|E|R|1|S]]|A|$]]|$1|F|3|G|5|6|7|T|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|U|8|@]|9|@]|A|$]]]|I|$J|$5|K|L|M|A|$N|C]]]]

I made a rails 3 gem for doing this that performs better on large tables and allows you to chain relations and scopes:

<a href="https://github.com/spilliton/randumb" rel="noreferrer">https://github.com/spilliton/randumb</a>

(edit): The default behavior of my gem basically uses the same approach as above now, but you have the option to use the old way if you want :)

blocks|key|964223|text|您可以在ActiveRecord中使用sample()|type|unstyled|depth|inlineStyleRanges|entityRanges|data|964224|例如。|964225|def+get_random_things_for_home_page
++find(:all).sample(5)
end|code-block|syntax|javascript|964226|来源：http://thinkingeek.com/2011/07/04/easily-select-random-records-rails/|offset|length|964227|entityMap|0|LINK|mutability|MUTABLE|url|http://thinkingeek.com/2011/07/04/easily-select-random-records-rails/^0|0|0|0|3|1X|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|V|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|W|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|X|8|@]|9|@$K|Y|L|Z|1|10]]|A|$]]|$1|M|3|-4|5|6|7|11|8|@]|9|@]|A|$]]]|N|$O|$5|P|Q|R|A|$S|T]]]]

You can use sample() in ActiveRecord

E.g.

<pre><code>def get_random_things_for_home_page
 find(:all).sample(5)
end
</code></pre>

Source: <a href="http://thinkingeek.com/2011/07/04/easily-select-random-records-rails/" rel="nofollow">http://thinkingeek.com/2011/07/04/easily-select-random-records-rails/</a>

blocks|key|748486|text|我在开发一个小应用程序时遇到了这个问题，在这个小应用程序中，我想从数据库中随机选择一个问题。我使用：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|748487|@question1+=+Question.where(:lesson_id+=>+params[:lesson_id]).shuffle[1]|code-block|syntax|javascript|748488|它对我来说运行得很好。我不能谈论大型数据库的性能，因为这只是一个小的应用程序。|748489|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

I just ran into this issue developing a small application where I wanted to select a random question from my DB. I used:

<pre><code>@question1 = Question.where(:lesson_id =&gt; params[:lesson_id]).shuffle[1]
</code></pre>

And it's working well for me. I can't speak on how the performance for larger DBs since this is just a small application.

blocks|key|748534|text|我们开始吧|type|unstyled|depth|inlineStyleRanges|entityRanges|data|748535|rails方式|748536|#in+your+initializer
module+ActiveRecord
++class+Base
++++def+self.random
++++++if+(c+=+count)+!=+0
++++++++find(:first,+:offset+=>rand(c))
++++++end
++++end
++end
end|code-block|syntax|javascript|748537|用法|748538|Model.random+#returns+single+random+object|748539|或者第二个想法是|748540|module+ActiveRecord
++class+Base
++++def+self.random
++++++order("RAND()")
++++end
++end
end|748541|用法：|748542|Model.random+#returns+shuffled+collection|748543|entityMap^0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|X|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Y|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|Z|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|10|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|11|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|12|8|@]|9|@]|A|$G|H]]|$1|Q|3|R|5|6|7|13|8|@]|9|@]|A|$]]|$1|S|3|T|5|F|7|14|8|@]|9|@]|A|$G|H]]|$1|U|3|-4|5|6|7|15|8|@]|9|@]|A|$]]]|V|$]]

here we go

<h1>rails way</h1>

<pre><code>#in your initializer
module ActiveRecord
 class Base
 def self.random
 if (c = count) != 0
 find(:first, :offset =&gt;rand(c))
 end
 end
 end
end
</code></pre>

<h1>usage</h1>

<pre><code>Model.random #returns single random object
</code></pre>

or the second thought is

<pre><code>module ActiveRecord
 class Base
 def self.random
 order("RAND()")
 end
 end
end
</code></pre>

usage:

<pre><code>Model.random #returns shuffled collection
</code></pre>

blocks|key|964469|text|从表中获取多个随机记录的一种非常简单的方法。这就产生了两个廉价的查询。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|964470|Model.where(id:+Model.pluck(:id).sample(3))|offset|length|style|CODE|964471|您可以将"3“更改为您想要的随机记录数。|964472|entityMap^0|0|0|17|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@$D|N|E|O|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|P|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|K|$]]

A very easy way to get multiple random records from the table. This makes 2 cheap queries.

<code>Model.where(id: Model.pluck(:id).sample(3))</code>

You can change the "3" to the number of random records you want.

blocks|key|964550|text|张贴的许多答案在相当大的表(1%2B百万行)上实际上不能很好地执行。随机排序很快就需要几秒钟，并且对表进行计数也需要相当长的时间。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|964551|在这种情况下，一个适合我的解决方案是使用带有where条件的RANDOM()：|offset|length|style|CODE|964552|Thing.where('RANDOM()+>=+0.9').take|code-block|syntax|javascript|964553|对于超过一百万行的表，此查询通常所需的时间不到2ms。|964554|entityMap^0|0|U|8|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|R|8|@$D|S|E|T|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|U|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|V|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

Many of the answers posted actually won't perform well on rather large tables (1+ million rows). Random ordering quickly takes a few seconds, and doing a count on the table also takes quite long.

A solution that works well for me in this situation is to use <code>RANDOM()</code> with a where condition:

<pre><code>Thing.where('RANDOM() &gt;= 0.9').take
</code></pre>

On a table with over a million rows, this query generally takes less than 2ms.

blocks|key|749145|text|从列表中随机选择一项的Ruby方法是sample。想要为ActiveRecord创建一个高效的sample，并基于前面的答案，我使用：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|749146|module+ActiveRecord
++class+Base
++++def+self.sample
++++++offset(rand(size)).first
++++end
++end
end|code-block|syntax|javascript|749147|我将它放在lib/ext/sample.rb中，然后在config/initializers/monkey_patches.rb中加载它|749148|Dir[Rails.root.join('lib/ext/*.rb')].each+{+%7Cfile%7C+require+file+}|749149|entityMap^0|I|6|1B|6|0|0|5|H|R|11|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]|$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|V|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|M|3|N|5|H|7|11|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|12|8|@]|D|@]|E|$]]]|P|$]]

The Ruby method for randomly picking an item from a list is <code>sample</code>. Wanting to create an efficient <code>sample</code> for ActiveRecord, and based on the previous answers, I used:

<pre><code>module ActiveRecord
 class Base
 def self.sample
 offset(rand(size)).first
 end
 end
end
</code></pre>

I put this in <code>lib/ext/sample.rb</code> and then load it with this in <code>config/initializers/monkey_patches.rb</code>:

<pre><code>Dir[Rails.root.join('lib/ext/*.rb')].each { |file| require file }
</code></pre>

blocks|key|964703|text|如果使用Postgres|type|unstyled|depth|inlineStyleRanges|entityRanges|data|964704|User.limit(5).order("RANDOM()")|code-block|syntax|javascript|964705|如果使用MySQL|964706|User.limit(5).order("RAND()")|964707|在这两个实例中，您都从Users表中随机选择了5条记录。以下是控制台中显示的实际SQL查询。|964708|SELECT+*+FROM+users+ORDER+BY+RANDOM()+LIMIT+5|964709|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|U|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

If using Postgres

<pre><code>User.limit(5).order("RANDOM()")
</code></pre>

If using MySQL

<pre><code>User.limit(5).order("RAND()")
</code></pre>

In both instances you're selecting 5 records randomly from the Users table. Here is the actual SQL query in displayed in the console.

<pre><code>SELECT * FROM users ORDER BY RANDOM() LIMIT 5
</code></pre>

blocks|key|964754|text|如果使用Oracle|type|unstyled|depth|inlineStyleRanges|entityRanges|data|964755|User.limit(10).order("DBMS_RANDOM.VALUE")|code-block|syntax|javascript|964756|输出|964757|SELECT+*+FROM+users+ORDER+BY+DBMS_RANDOM.VALUE+WHERE+ROWNUM+<=+10|964758|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

If using Oracle

<pre><code>User.limit(10).order("DBMS_RANDOM.VALUE")
</code></pre>

Output

<pre><code>SELECT * FROM users ORDER BY DBMS_RANDOM.VALUE WHERE ROWNUM &lt;= 10
</code></pre>

blocks|key|749381|text|可以在Rails+5中工作，并且与DB无关：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|749382|在你的控制器中：|749383|@quotes+=+Quote.offset(rand(Quote.count+-+3)).limit(3)|code-block|syntax|javascript|749384|当然，您可以将此放入一个关注中，如here所示。|offset|length|749385|应用程序/模型/关注点/随机性.rb|749386|module+Randomable
++extend+ActiveSupport::Concern

++class_methods+do
++++def+random(the_count+=+1)
++++++records+=+offset(rand(count+-+the_count)).limit(the_count)
++++++the_count+==+1+?+records.first+:+records
++++end
++end
end|749387|然后..。|749388|app/model/book.rb|749389|class+Book+<+ActiveRecord::Base
++include+Randomable
end|749390|然后，您可以通过执行以下操作来简单地使用：|749391|Books.random|749392|或|749393|Books.random(3)|749394|entityMap|0|LINK|mutability|MUTABLE|url|http://sebastien.saunier.me/blog/2015/11/04/retrieve-a-random-record-in-a-rails-application.html^0|0|0|0|H|4|0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1C|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1D|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|1E|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|1F|8|@]|9|@$K|1G|L|1H|1|1I]]|A|$]]|$1|M|3|N|5|6|7|1J|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|1K|8|@]|9|@]|A|$G|H]]|$1|Q|3|R|5|6|7|1L|8|@]|9|@]|A|$]]|$1|S|3|T|5|6|7|1M|8|@]|9|@]|A|$]]|$1|U|3|V|5|F|7|1N|8|@]|9|@]|A|$G|H]]|$1|W|3|X|5|6|7|1O|8|@]|9|@]|A|$]]|$1|Y|3|Z|5|F|7|1P|8|@]|9|@]|A|$G|H]]|$1|10|3|11|5|6|7|1Q|8|@]|9|@]|A|$]]|$1|12|3|13|5|F|7|1R|8|@]|9|@]|A|$G|H]]|$1|14|3|-4|5|6|7|1S|8|@]|9|@]|A|$]]]|15|$16|$5|17|18|19|A|$1A|1B]]]]

Works in Rails 5 and is DB agnostic:

This in your controller:

<pre><code>@quotes = Quote.offset(rand(Quote.count - 3)).limit(3)
</code></pre>

You can, of course, put this in a concern as shown <a href="http://sebastien.saunier.me/blog/2015/11/04/retrieve-a-random-record-in-a-rails-application.html" rel="nofollow noreferrer">here</a>.

<h1>app/models/concerns/randomable.rb</h1>

<pre><code>module Randomable
 extend ActiveSupport::Concern

 class_methods do
 def random(the_count = 1)
 records = offset(rand(count - the_count)).limit(the_count)
 the_count == 1 ? records.first : records
 end
 end
end
</code></pre>

then...

<h1>app/models/book.rb</h1>

<pre><code>class Book &lt; ActiveRecord::Base
 include Randomable
end
</code></pre>

Then you can use simply by doing:

<pre><code>Books.random
</code></pre>

or 

<pre><code>Books.random(3)
</code></pre>

So, I've found several examples for finding a random record in Rails 2 -- the preferred method seems to be:

<pre><code>Thing.find :first, :offset =&gt; rand(Thing.count)
</code></pre>

Being something of a newbie I'm not sure how this could be constructed using the new find syntax in Rails 3.

So, what's the "Rails 3 Way" to find a random record?

Rails 3: Get Random Record

PostgreSQL

数据库

MySQL

因此，我找到了几个在Rails 2中查找随机记录的示例--首选的方法似乎是：Thing.find :first, :offset => rand(Thing.count)作为一个新手，我不确定这是如何使用Rails3中新的find语法构建的。那么，找到随机记录的“Rails3方法”是什么呢？

问Rails 3:获取随机记录
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