I was just solving issue, where I needed to keep an order of items returned from the MySQL database listen in the WHERE IN clause.
Original query:

SELECT * FROM table WHERE id IN (1,5,8,73,5,4,88)

This will return rows ordered by its primary key (in my case column id). Here is updated query, which will keep order of items listed in WHERE IN clause:

SELECT * FROM table WHERE id IN (1,5,8,73,5,4,88) ORDER BY FIELD(id,1,5,8,73,5,4,88)

Please note first item in brackets behind ORDER BY – there should be set same column, which was used at WHERE IN clause.

UPDATE: There was missing function called FIELD after ORDER BY – code is fixed now.