create table T1(
SL int NOT NULL IDENTITY (1, 1),
ISDN varchar(13) NULL,
MSG varchar(50) NULL
)

insert into T1(ISDN,MSG) values ('123','ABC');
insert into T1(ISDN,MSG) values ('123','ABC');
insert into T1(ISDN,MSG) values ('123','XYZ');
insert into T1(ISDN,MSG) values ('124','XYZ');
insert into T1(ISDN,MSG) values ('124','EFG');

create table #T1(
SL int NOT NULL IDENTITY (1, 1),
ISDN varchar(13) NULL,
MSG varchar(50) NULL
)

insert into #T1(ISDN,MSG) values ('123','ABC');
insert into #T1(ISDN,MSG) values ('123','ABC');
insert into #T1(ISDN,MSG) values ('123','XYZ');
insert into #T1(ISDN,MSG) values ('124','XYZ');
insert into #T1(ISDN,MSG) values ('124','EFG');

--extra duplicate added for better illustration
insert into #T1(ISDN,MSG) values ('123','ABC');


WITH CTE AS (
select row_number() over(partition by isdn, msg order by isdn, msg) as instanceNumber,
SL, ISDN, MSG
from #t1
)


select lt.* from cte as lt inner join (select * from cte where instanceNumber=2) as rt
	on lt.isdn=rt.isdn and lt.msg=rt.msg and lt.instanceNumber=1
union all
select * from cte where instanceNumber>1


drop table #t1

select
	'Yes' as ARE_THE_SAME,
a.*
from #T1 a
left join #T1 b on a.sl<>b.sl and a.isdn=b.isdn and a.msg=b.msg
where b.sl is not null

select ISDN, MSG, count(*) 
from #t1
group by ISDN, MSG
having count(*) > 1