SQL Server 2019

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.

SELECT * INTO Data
FROM
(
  VALUES
  (1,    'aaa',          0,        0),   
  (2,    'aaa',          1,        0), 
  (3,    'aaa',          0,        0), 
  (4,    'bbb',          0,        0),   
  (5,    'bbb',          0,        0), 
  (6,    'bbb',          0,        0)
)T(Id,   groupName,    flag,    type );
6 rows affected

UPDATE D
SET Type = 1
FROM Data D JOIN
(
  SELECT GroupName
  FROM Data
  WHERE Flag = 1
) T ON D.GroupName = T.GroupName;

3 rows affected

SELECT *
FROM Data;


Id
groupName
flag
type


1
aaa
0
1

2
aaa
1
1

3
aaa
0
1

4
bbb
0
0

5
bbb
0
0

6
bbb
0
0