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)



declare @t table (custID int, prodID int, title varchar(100), titleCount int, isMasterTitle int)

insert into @t select 266 , 191750 ,'prod01' , 1 , 0
insert into @t select 266 , 191750 ,'prod01' , 4 , 0
insert into @t select 266 , 191750 ,'prod01' , 25 , 0
insert into @t select 300 , 20125 , 'prod02' , 3 , 0
insert into @t select 300 , 20125 , 'prod02' , 15 , 0

select * from @t

;with cte 
as
(
	select custID, prodID, title, titleCount, ROW_NUMBER() over (partition by custID, prodID, title order by titleCount desc) rn
	from @t
)
update t
set isMasterTitle = 1
from @t t
join cte on t.custID = cte.custID and t.prodID = cte.prodID and t.title = cte.title and t.titleCount = cte.titleCount and rn = 1

select * from @t


custID
prodID
title
titleCount
isMasterTitle


266
191750
prod01
1
0

266
191750
prod01
4
0

266
191750
prod01
25
0

300
20125
prod02
3
0

300
20125
prod02
15
0




custID
prodID
title
titleCount
isMasterTitle


266
191750
prod01
1
0

266
191750
prod01
4
0

266
191750
prod01
25
1

300
20125
prod02
3
0

300
20125
prod02
15
1


declare @t table (custID int, prodID int, title varchar(100), titleCount int, isMasterTitle int)

insert into @t select 266 , 191750 ,'prod01' , 1 , 0
insert into @t select 266 , 191750 ,'prod01' , 4 , 0
insert into @t select 266 , 191750 ,'prod01' , 25 , 0
insert into @t select 300 , 20125 , 'prod02' , 3 , 0
insert into @t select 300 , 20125 , 'prod02' , 15 , 0

select * from @t

UPDATE @t
SET isMasterTitle = 1
FROM @t  v1
INNER JOIN (SELECT custID, prodID, title, MAX(titleCount) AS mtitleCount 
            FROM @t 
            GROUP BY custID,prodID, title) as v2 ON v1.custID = v2.custID and v1.prodID = v2.prodID and v1.title = v2.title and v1.titleCount = v2.mtitleCount

select * from @t


custID
prodID
title
titleCount
isMasterTitle


266
191750
prod01
1
0

266
191750
prod01
4
0

266
191750
prod01
25
0

300
20125
prod02
3
0

300
20125
prod02
15
0




custID
prodID
title
titleCount
isMasterTitle


266
191750
prod01
1
0

266
191750
prod01
4
0

266
191750
prod01
25
1

300
20125
prod02
3
0

300
20125
prod02
15
1
custID	prodID	title	titleCount
266	191750	prod01	1
266	191750	prod01	4
266	191750	prod01	25
300	20125	prod02	3
300	20125	prod02	15