Last record per range extended, MySQL

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#MySQL 5.7.12
#please drop objects you've created at the end of the script 
#or check for their existance before creating
#'\\' is a delimiter

drop table if exists attendance\\
create table if not exists attendance(atid int, atdate date, attime time, atuserid int, atreaderid int)\\

insert into attendance values(64315, '2017-01-17', '10:11:40', 856, 1102)\\
insert into attendance values(66450, '2017-01-17', '14:05:10', 856, 101)\\
insert into attendance values(66776, '2017-01-17', '15:03:40', 856, 1102)\\
insert into attendance values(67104, '2017-01-17', '16:04:20', 856, 101)\\
insert into attendance values(67161, '2017-01-18', '08:22:40', 856, 1102)\\
insert into attendance values(67165, '2017-01-18', '09:21:00', 856, 1102)\\
insert into attendance values(68620, '2017-01-18', '12:14:10', 856, 101)\\
insert into attendance values(68621, '2017-01-18', '12:14:10', 856, 1101)\\
insert into attendance values(68622, '2017-01-18', '12:14:20', 856, 1101)\\
insert into attendance values(68623, '2017-01-18', '12:14:20', 856, 1101)\\
insert into attendance values(68624, '2017-01-18', '12:14:20', 856, 1101)\\
insert into attendance values(68625, '2017-01-18', '12:14:20', 856, 1101)\\
insert into attendance values(68626, '2017-01-18', '12:14:30', 856, 1101)\\
insert into attendance values(68627, '2017-01-18', '12:14:30', 856, 102)\\
insert into attendance values(68628, '2017-01-18', '12:14:40', 856, 1102)\\

select
  atid, atdate, attime, atuserid, atreaderid
from
(
	select 
		atid, atdate, attime, atuserid, atreaderid, 
		(atreaderid div 1000 <> @after div 1000) as keepit,
		@after := atreaderid
	from attendance
	cross join (select @after := 2000) var
	where atuserid = 856 and atreaderid in (101, 102, 1101, 1102)
	order by timestamp(atdate, attime) desc, atid desc
) marked
where keepit
order by timestamp(atdate, attime), atid\\

drop table attendance\\


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