Rails Postgresql sort by random

Question

I am trying to pull out rows from a postgres database, I can pull them out desc but when I try random I get a Syntax error near random.

Error

PG::Error: ERROR:  syntax error at or near "rand"
LINE 1: ...  "hashtags".* FROM "hashtags"  ORDER BY tweet_id rand LIMIT...
                                                             ^
: SELECT  "hashtags".* FROM "hashtags"  ORDER BY tweet_id rand LIMIT 4

Code to pull it out

<div id="hashtags">
<% Hashtag.order("tweet_id desc").limit(4).each do |hashtag| %>
   <blockquote><%= hashtag.content %></blockquote>
   <div class="from">&mdash; @<%= hashtag.screen_name %></div>
 <% end %>
</div>

Answer 1

To fetch random entries from your database you have a few options. Here's a couple

1st approach

This will take 4 random entries out of your DB using SQL.

Hashtag.order("RANDOM()").limit(4)

2nd approach:

You can also use ActiveRecord sample() method to retrieve 4 random rows.

Hashtag.all.sample(4)

As of speed and efficiency; I made a mini-benchmark and tested two commands on my own db (contains 500 records). The first approach (as expected) was more than twice faster than the second approach.

SQL: 1.8ms
Sample Method: 4.2ms