SQL: Query to set value based on group parameter

Question

I need help writing a query to do the following on a table in my DB:

Select all rows where the values in Column1 are the same
    If a 'Primary' has not been set in Column2 for any of them
        Set Column2 = 'Primary' for first row in the group 
    Else go on to the next group 

Key points: I can only have one 'Primary' tag per group

Sample input:

Column1 | Column2 | 
ID1                 
ID1                       
ID1                     
ID2       Primary
ID2       
ID3       
ID3       

Sample Result:

Column1 | Column2 | 
ID1       Primary         
ID1                       
ID1                     
ID2       Primary
ID2       
ID3       Primary   
ID3       

Thank you!

Answer 1

SELECT Column1  
     ,CASE 
        WHEN ROW_NUMBER() OVER (PARTITION BY Column1 ORDER BY [TargetColumn]) = 1 
          THEN  'Primary' 
          ELSE '' 
     END AS Column2
FROM TableName

TargetColumn will be the column that will decide in each group of Column1 which Value is the Primary Value.

Answer 2

Use ROW_NUMER window function to find the first record per group then update only the records which doesnot have primary value in column2

Since there is no column available to find the first record per group i have used (select null) in order by

Sample data

CREATE TABLE #ee(Column1 VARCHAR(50),Column2 VARCHAR(50))

INSERT #ee
VALUES ('ID1',NULL),
       ('ID1',NULL),
       ('ID1',NULL),
       ('ID2','Primary'),
       ('ID2',NULL),
       ('ID3',NULL),
       ('ID3',NULL) 

Update query:

;WITH cte
     AS (SELECT *,
                Row_number()OVER(partition BY column1 ORDER BY (SELECT NULL)) RN
         FROM   #ee a
         WHERE  NOT EXISTS (SELECT 1
                            FROM   #ee b
                            WHERE  a.Column1 = b.Column1
                                   AND b.Column2 = 'primary'))
UPDATE cte
SET    Column2 = 'primary'
WHERE  rn = 1 

Result:

Column1 Column2
------- -------
ID1     primary
ID1     NULL
ID1     NULL
ID2     Primary
ID2     NULL
ID3     primary
ID3     NULL