MySQL: Get unique values across multiple columns in alphabetical order

Question

If my table looks like this:

id | colA   | colB | colC
===========================
1  | red    | blue | yellow
2  | orange | red  | red
3  | orange | blue |          


        

Answer 1

(SELECT DISTINCT colA AS color FROM table) UNION
(SELECT DISTINCT colB AS color FROM table) UNION
(SELECT DISTINCT colC AS color FROM table)
ORDER BY color