CREATE PARTITION FUNCTION MyIntDatePartFunc (int) AS RANGE RIGHT FOR VALUES ('20140101', '20140201', ... , '20251201', '20260101');

select max($PARTITION.MyIntDatePartFunc(KEY_DATE_START)), min($PARTITION.MyIntDatePartFunc(KEY_DATE_START)), min(key_date_start), max(key_date_start) from TMP_F_table

([KEY_DATE_START]>=(20180101) AND [KEY_DATE_START]<(20180132))

ALTER TABLE TMP_F_table WITH CHECK CHECK CONSTRAINT all

CREATE PARTITION FUNCTION MyIntDatePartFunc (int) 
AS RANGE RIGHT FOR VALUES ('20180101', '20180201', '20180301', '20180401');
GO

create partition scheme MyIntDatePartSch
as partition MyIntDatePartFunc to
([primary],[primary],[primary],[primary],[primary]);

create table dbo.test(KEY_DATE_START int not null) on MyIntDatePartSch(KEY_DATE_START);

create table TMP_F_table(KEY_DATE_START int not null) on MyIntDatePartSch(KEY_DATE_START);
insert into TMP_F_table values (20180101), (20180131);

select $Partition.MyIntDatePartFunc (20180101);
---
--2

alter table TMP_F_table switch partition 2 to dbo.test partition 2;
-- Command(s) completed successfully.

alter table dbo.test switch partition 2 to TMP_F_table partition 2;
-- Command(s) completed successfully.

alter table TMP_F_table add constraint CK_int
check ([KEY_DATE_START]>=(20180101) AND [KEY_DATE_START]<(20180132));

alter table TMP_F_table switch partition 2 to dbo.test partition 2;
-- Command(s) completed successfully.

alter table dbo.test switch partition 2 to TMP_F_table partition 2;

declare @int int = 20180199
select case when @int between '20180101' and '20180201' then 'yes' else 'no' end
---
yes