Order results in which it was read in. Using in() - mysql

Question

This is my query in mysql:
SELECT school_id, first_name, last_name, email, blog_username, comment_username
FROM table
WHERE user_id IN (100, 3,72) ;
The results show the two user_id's in ascending order. How can I make it so that it is ordered by in which is was received?
So instead of 3, 72, 100 I want the results to be 100, 3, 72.

Answer 1

Select school_id, first_name, last_name, email, blog_username, comment_username
From table
Where user_id IN ( 100, 3, 72 )
Order By Case
When user_id = 100 Then 1
When user_id = 3 Then 2
When user_id = 72 Then 3
End Asc
Addition explanation:
What is being sought is the ability to order the rows in a custom manner. Said another way, we need to add custom cardinality to a set of values that do not conform to a standard cardinality. A Case expression can be used to do just that. Another way to accomplish the same thing would be:
Select school_id, first_name, last_name, email, blog_username, comment_username
From table
Join (
Select 100 As user_id, 1 As Sort
Union All Select 3, 2
Union All Select 72, 3
) As Seq
On Seq.user_id = table.user_id
Order By Seq.Sort

Answer 2

MySQL has a function FIELD() which is suited for this:
ORDER BY FIELD(user_id, 100, 3, 72 )
http://dev.mysql.com/doc/refman/5.6/en/string-functions.html#function_field
and in general (method is designed for strings but it will work just fine with numbers)
ORDER BY FIELD(field_name, value_1, value_2, ... )
However
It makes your SQL less portable
Ordering like this is much less efficient
Whole code
SELECT school_id, first_name, last_name, email, blog_username, comment_username
FROM table
WHERE user_id IN (100, 3, 72)
ORDER BY FIELD(user_id, 100, 3, 72)
Although I would consider changing the rest of you code so you do not have to use this method.