SQL Server 2017

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Create table Customer_info
(Customer_num  varchar(50),
 Customer_Branch  int);

Create table Customer_Transaction_Info
(Customer_num     varchar(50),
 Branch_Code      int,
 Trns_Measure_One int,
 Trns_Measure_Two int
 );
 
insert into Customer_info(Customer_num , Customer_Branch)
values('A',1),
      ('B',2),
      ('C',3);
      
insert into Customer_Transaction_Info (Customer_num,Branch_Code,Trns_Measure_One,Trns_Measure_Two)
Values ('A',1,10,0),
       ('A',2,20,5),
       ('A',3,14,0),
       ('B',2,10,10),
       ('B',1,36,0),
       ('C',3,14,0),
       ('C',1,10,18);
       
SELECT * FROM Customer_info;
SELECT * FROM Customer_Transaction_Info;


Customer_num
Customer_Branch


A
1

B
2

C
3




Customer_num
Branch_Code
Trns_Measure_One
Trns_Measure_Two


A
1
10
0

A
2
20
5

A
3
14
0

B
2
10
10

B
1
36
0

C
3
14
0

C
1
10
18


-- look at correct state
SELECT cti.Customer_num, cti.Branch_Code, cti.Trns_Measure_One,
       CASE WHEN ci.Customer_Branch = cti.Branch_Code
            THEN MAX(cti.Trns_Measure_Two) OVER (PARTITION BY cti.Customer_num)
            ELSE 0
            END Trns_Measure_Two
FROM Customer_info ci
JOIN Customer_Transaction_Info cti ON ci.Customer_num = cti.Customer_num


Customer_num
Branch_Code
Trns_Measure_One
Trns_Measure_Two


A
1
10
5

A
2
20
0

A
3
14
0

B
2
10
10

B
1
36
0

C
3
14
18

C
1
10
0


-- update for correct state
UPDATE Customer_Transaction_Info
SET Trns_Measure_Two = subquery.Trns_Measure_Two
FROM (SELECT cti.Customer_num, cti.Branch_Code, cti.Trns_Measure_One,
             CASE WHEN ci.Customer_Branch = cti.Branch_Code
                  THEN MAX(cti.Trns_Measure_Two) OVER (PARTITION BY cti.Customer_num)
                  ELSE 0
                  END Trns_Measure_Two
      FROM Customer_info ci
      JOIN Customer_Transaction_Info cti ON ci.Customer_num = cti.Customer_num) subquery
WHERE Customer_Transaction_Info.Customer_num = subquery.Customer_num
  AND Customer_Transaction_Info.Branch_Code = subquery.Branch_Code
7 rows affected

-- see the result
SELECT * FROM Customer_Transaction_Info;


Customer_num
Branch_Code
Trns_Measure_One
Trns_Measure_Two


A
1
10
5

A
2
20
0

A
3
14
0

B
2
10
10

B
1
36
0

C
3
14
18

C
1
10
0