Just had to combine two tables month column and sort the whole thing. I had two tables like
and I wanted (put the two tables‘ month in one column and remove duplicates):
The solution was not too complicated, but I thought I share it.
SELECT MONTH FROM table1 UNION SELECT MONTH FROM table2 ORDER BY MONTH DESC
No need to add a GROUP BY because of the UNION, and the seconds query ORDER BY sorts the complete result.