SQL Server 2019

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select @@version;

(No column name)
Microsoft SQL Server 2019 (RTM-CU3) (KB4538853) - 15.0.4023.6 (X64) Mar 4 2020 00:59:26 Copyright (C) 2019 Microsoft Corporation Express Edition (64-bit) on Windows Server 2019 Standard 10.0 <X64> (Build 17763: ) (Hypervisor)

create table SampleTable( col1 varchar(10)

, col2 varchar(10)

, col3 bit)

insert into SampleTable values

('abc', 'xyz', 0),

('abc', 'xyz', 1),

('abc', 'xyz', 0),

('mno', 'xyz', 0),

('mno', 'xyz', 1)

--Before update

select * from SampleTable

--Getting rows with duplicate

; with cte as (SELECT col1

, col2

, col3

, row_number() over (partition by col1, col2, col3 order by (select null)) as cnt

FROM SampleTable

)UPDATE t

set t.col1 = t.col1

, t.col2 = t.col2

, t.col3 = 1

from SampleTable t

inner join cte on t.col1 = cte.col1

and t.col2 = cte.col2 and t.col3 = cte.col3

and cnt > 1

--After update

select * from SampleTable