MySQL union order by sorting issues separately

Two different ways:

The first type:

Sort them first, and then merge the results with the temporary table nesting, noting that the order must be preceded by a limit, otherwise the order by does not work

SELECT * FROM (SELECT * to T1 WHERE ID in (1,3,6) ORDER by Utime DESC limit 5) as a
UNION All
SELECT * FROM (SELECT * to T1 WHERE ID in (2,4,5) ORDER by Utime DESC limit 5) as B
;
The second type:

After all results are detected by adding a temporary column px, then sort by px,utime

SELECT * FROM (
Select 0 as Px,id,name,utime from (SELECT * from T1 WHERE ID in (1,3,6)) as a
UNION All
Select 1 as Px,id,name,utime from (SELECT * from T1 WHERE ID in (2,4,5)) as B
) as C ORDER by Px,utime DESC

MySQL union order by sorting issues separately