Rails 3:获取随机记录 [英] Rails 3: Get Random Record

问题描述

因此，我找到了几个在 Rails 2 中查找随机记录的示例——首选方法似乎是:

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

Thing.find :first, :offset => rand(Thing.count)

作为一个新手，我不确定如何使用 Rails 3 中的新 find 语法来构建它.

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

那么，查找随机记录的Rails 3 方法"是什么?

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

推荐答案

Thing.first(:order => "RANDOM()") # For MySQL :order => "RAND()", - thanx, @DanSingerman
# Rails 3
Thing.order("RANDOM()").first

或

Thing.first(:offset => rand(Thing.count))
# Rails 3
Thing.offset(rand(Thing.count)).first

实际上，在 Rails 3 中，所有示例都可以使用.但是使用 RANDOM 命令对于大表来说很慢，但更多的是 sql-style

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

更新.您可以在索引列上使用以下技巧(PostgreSQL 语法):

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

select * 
from my_table 
where id >= trunc(
  random() * (select max(id) from my_table) + 1
) 
order by id 
limit 1;

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