SQL grouping by month and year

SELECT CAST(MONTH(date) AS VARCHAR(2)) + '-' + CAST(YEAR(date) AS VARCHAR(4)) AS Mjesec, SUM(marketingExpense) AS SumaMarketing, SUM(revenue) AS SumaZarada 
FROM [Order]
WHERE (idCustomer = 1) AND (date BETWEEN '2001-11-3' AND '2011-11-3')
GROUP BY CAST(MONTH(date) AS VARCHAR(2)) + '-' + CAST(YEAR(date) AS VARCHAR(4))

Or as @40-Love mentioned you can cast with leading zeroes:

GROUP BY 
  CAST(YEAR(date) AS VARCHAR(4)) + '-' + right('00' + CAST(MONTH(date) AS VARCHAR(2)), 2) 

I'm guessing this is MS SQL, as it looks like MS SQL syntax.

You should put the same thing in the group by as you have in the select.

For example:

Select MONTH(date)+'-'+YEAR(date), ....
...
...
...
group by MONTH(date)+'-'+YEAR(date)