ORDER BY column OFFSET 0 ROWS
Surprisingly makes it work, what a strange feature.
A bigger example with a CTE as a way to temporarily "store" a long query to re-order it later:
;WITH cte AS (
SELECT .....long select statement here....
)
SELECT * FROM
(
SELECT * FROM
( -- necessary to nest selects for union to work with where & order clauses
SELECT * FROM cte WHERE cte.MainCol= 1 ORDER BY cte.ColX asc OFFSET 0 ROWS
) first
UNION ALL
SELECT * FROM
(
SELECT * FROM cte WHERE cte.MainCol = 0 ORDER BY cte.ColY desc OFFSET 0 ROWS
) last
) as unionized
ORDER BY unionized.MainCol desc -- all rows ordered by this one
OFFSET @pPageSize * @pPageOffset ROWS -- params from stored procedure for pagination, not relevant to example
FETCH FIRST @pPageSize ROWS ONLY -- params from stored procedure for pagination, not relevant to example
So we get all results ordered by MainCol
But the results with MainCol = 1 get ordered by ColX
And the results with MainCol = 0 get ordered by ColY