Change the COLLATE for one of the columns.

Try this:

create table my_table(id1 nvarchar(10), id2 varchar(10))

SELECT TABLE_NAME, COLUMN_NAME,CHARACTER_SET_NAME, COLLATION_NAME

FROM information_schema.columns

WHERE TABLE_NAME = 'my_table'

insert into my_table VALUES ('-1','-1');

insert into my_table VALUES ('1','1');

SELECT MAX(id1 COLLATE Latin1_General_Bin2), MAX(id2)

FROM my_table

DROP table my_table

You can see from the first SELECT that these columns have the same COLLATE sequence but different character sets. Changing to a binary collation resolves the issue you inquired about. Be warned that it may also cause other undesired side effects (test, test, test!).