How to "push ahead" records with a given value? - mysql

Question

I am using Ruby on Rails 3.2.9 and MySQL. I have an Article model with a user_id attribute (this attribute represents the foreign key - id - for associated author users) and I would like to retrieve articles ordering those "for" a given author. That is, given I have following records:
<#Article id: 1, title: "Title 1", user_id: 1>
<#Article id: 2, title: "Title 2", user_id: 2>
<#Article id: 3, title: "Title 3", user_id: 1>
<#Article id: 4, title: "Title 4", user_id: 3>
<#Article id: 5, title: "Title 5", user_id: 1>
...
<#Article id: N, title: "Title N", user_id: M>
When I look for articles ordered "for" the author with id 1 (user_id = 1) then the returning articles should be ordered as-like the following:
<#Article id: 1, title: "Title 1", user_id: 1>
<#Article id: 3, title: "Title 3", user_id: 1>
<#Article id: 5, title: "Title 5", user_id: 1>
<#Article id: 2, title: "Title 2", user_id: 2>
<#Article id: 4, title: "Title 4", user_id: 3>
...
<#Article id: N, title: "Title N", user_id: M>
In other words, I am looking to retrieve all articles but making those ordered with this "priority": articles created by the given author returned first and then all other articles (that is, I would like to "push ahead" articles created by a given author).
How can I make that?
Note: I am looking for a Ruby on Rails implementation, maybe through the order method.

Answer 1

Your example is not that clear since you are searching for user_id 1 and a normal ordering by user_id would put those first anyway. I believe you mean to do something like:
SELECT id, title, user_id
FROM myTable
ORDER BY CASE WHEN user_id = #search_id THEN 1 ELSE 2 END, user_id
In your example above, #search_id should be 1.

Answer 2

Try:
Article.where(user_id: 1).order("user_id ASC").order("id ASC")
Or this:
Article.where(user_id: 1).order("user_id ASC, id ASC")

Answer 3

Try this ::
Select
*
from
myTable
order by
user_id, id
For a given user_id:
Select
*
from
myTable
where user_id='?'
order by
user_id, id

Answer 4

The query in Rails could be like this:
Article.order(Article.send(:sanitize_sql, ["IF(user_id = ?, 1, 2)", params[:user_id]]))
IF(user_id = ?, 1, 2) returns 1 or 2 for ordering articles. sanitize_sql, a private method, is used to sanitize parameters.
If params[:user_id] is always an integer, the query could be simplified to this:
Article.order("IF(user_id = #{params[:user_id].to_i}, 1, 2)")