test, Sql Server - rextester

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--Sql Server 2014 Express Edition
--Batches are separated by 'go'

create table mytable (group_type varchar(2), desk_number int, comments varchar(5))

insert into mytable values ('a1', 5, 'qwe')
                           ,('a1', 4, 'dfd')
                           ,('a1', 3, 'asd')
                           ,('a1', 5, 'uid')
                           ,('a1', 5, 'xme')
                           ,('b1', 6, 'dkr')
                           ,('b1', 4, 'qpd')
                           ,('b1', 3, 'cif')
                           ,('b1', 6, 'edd')
                           ,('b1', 6, 'dkr')
                           ,('b1', 6, 'mdl')
                           ,('c1', 3, 'dls')
                           ,('c1', 1, 'ckc')
                           ,('c1', 2, 'cxl')
                           ,('c1', 3, 'sdl')
                           ,('c1', 3, 'slwl')
                           ,('c1', 3, 'dcl')
                           ,('c1', 1, 'skc')

select group_type
       ,desk_number
       ,comments
from
(select *
       ,dense_rank() over(partition by group_type order by desk_number desc) dr
from mytable) t1
where t1.dr = 1

View schema
Execution time: 0,02 sec, rows selected: 11, rows affected: 18, absolute service time: 0,19 sec