How does sql UNION can combine the ORDER BY result?

Question

I used sql1: Select * From my_table Where column_a='aa' Order By column_b desc Limit 2.
And I used sql2: Select * From my_table_2 Where column_a='bb' Order By column_b desc Limit 2.
Then I combined the result like this:
Select * From my_table Where column_a='aa' Order By column_b desc Limit 2
Union
Select * From my_table_2 Where column_a='bb' Order By column_b desc Limit 2
The result is like this
column_a column_b
aa 15
aa 10
bb 21
bb 11
, but I want the result like this
column_a column_b
bb 21
aa 15
bb 11
aa 10
Is there any way to order by after union. Thanks.

Answer 1

SELECT *
FROM (
SELECT TOP 2 *
FROM my_table
ORDER BY column_b DESC
UNION ALL
SELECT TOP 2 *
FROM my_table_2
ORDER BY column_b DESC
) SubQuery
ORDER BY column_b DESC

Sorry if the syntax is a bit off. I'm most familiar with Microsoft SQL and don't have a DB readily available