Question

I have a MYSQL database with the following fields (simplified to show issue):

id | courseID | date1      | date2      | date 3     | date 4 
-----------------------------------------------------------------
1  | 10       | 2013-01-01 | 2013-02-05 | 0000-00-00 | 0000-00-00
2  | 23       | 2013-03-02 | 2013-05-04 | 2013-07-05 | 0000-00-00
3  | 35       | 2013-02-01 | 0000-00-00 | 0000-00-00 | 0000-00-00

My question is what query could I use to find all the courses with a date less than or equal to today in one of the four fields ordered by date descending. So for my database above the query would give me:

id  | courseID | date
---------------------------
1   | 10       | 2013-02-05
3   | 35       | 2013-02-01
1   | 10       | 2013-01-01

Many thanks for your help.

Answer 1

If you can’t normalize your table, you could use a UNION query, like this:

SELECT id, courseID, date1 date
FROM yourtable
WHERE date1>'0000-00-00' and date1<=curdate()
UNION
SELECT id, courseID, date2 date
FROM yourtable
WHERE date2>'0000-00-00' and date2<=curdate()
UNION
SELECT id, courseID, date3 date
FROM yourtable
WHERE date3>'0000-00-00' and date3<=curdate()
UNION
SELECT id, courseID, date4 date
FROM yourtable
WHERE date4>'0000-00-00' and date4<=curdate()
ORDER BY date

See fiddle here.

Since I am using UNION, all duplicates will be removed. If you don’t want to remove duplicates, you could use UNION ALL instead.