Q:

SQL: Order by date, only month and year given - Full Group on

I have an SQL database which is setted to full group on mode. My goal is to get the amount of rows (ID's) for every month. This is why I say Group By Datum. Because of the full group mode I cannot simply say Order By created_at. Because I have selected only %m.%Y. So I can only work with Datum which is cointaing my month and year.
I already tried to connect those values like CONCAT('DATE_FORMAT(created_at, '%Y-%m'), "-01 00:00:00") but also this isn't working... Even if I turn it into a UNIX Timestamp it isn't working: UNIX_TIMESTAMP(CONCAT('DATE_FORMAT(created_at, '%Y-%m'), "-01 00:00:00"))
I even tried this one:
Order By Year(DATE_FORMAT(created_at, '%Y')), Month DATE_FORMAT(created_at, '%m') But it isn't also working...
How can I sort my result by month and year without changing the Select values?
Sofar this is my actual SQL Query. Not working either.. I am nearly trying to find a solution since 1 hour...
SELECT COUNT(ID) AS Anzahl, DATE_FORMAT(created_at, '%m.%Y') AS Datum 
   FROM leads 
  WHERE created_at >= '2015-01-01' AND created_at <= '2018-01-01' 
    AND shopID = 4184 
GROUP BY Datum 
ORDER BY UNIX_TIMESTAMP(STR_TO_DATE(Datum, '%Y-%m-01 00:00:00'))
I would appreciate any kind of help! And no, I cannot change the Select values or turn off the full_group_mode.

A:

The following will sort by year and then month in ascending order:
order by substring(datum,4,4), substring(datum,1,2)

sqlfiddle:http://sqlfiddle.com/#!9/16fab4/3

