SQL Server 2012 First_Value Function - sql

Question

I am stuck in a case since 2 days and I need your assistance please.
the table as below :
Sample Table
SR UID Flag Fees
1 AAA 1 100.00
2 AAA 0 0.00
3 AAA 0 0.00
4 AAA 1 120.00
5 AAA 0 0.00
6 AAA 0 0.00
7 AAA 1 140.00
1 BBB 1 200.00
2 BBB 0 0.00
3 BBB 0 0.00
4 BBB 0 0.00
5 BBB 0 0.00
6 BBB 0 0.00
7 BBB 1 400.00
how I can use First_value function to replace the 0.00 values in fees column with the first value where Flag =1 partition by UID
the result should be as the following
Results
SR UID Flag Fees First_Value
1 AAA 1 100.00 100.00
2 AAA 0 0.00 100.00
3 AAA 0 0.00 100.00
4 AAA 1 120.00 120.00
5 AAA 0 0.00 120.00
6 AAA 0 0.00 120.00
7 AAA 1 140.00 140.00
1 BBB 1 200.00 200.00
2 BBB 0 0.00 200.00
3 BBB 0 0.00 200.00
4 BBB 0 0.00 200.00
5 BBB 0 0.00 200.00
6 BBB 0 0.00 200.00
7 BBB 1 400.00 400.00

Answer 1

One idea, using FIRST_VALUE like the Op was trying to:
CREATE TABLE #Sample (SR int, UID char(3), Flag bit, Fees decimal(5,2));
INSERT INTO #Sample
VALUES
(1,'AAA',1,100.00),
(2,'AAA',0,0.00 ),
(3,'AAA',0,0.00 ),
(4,'AAA',1,120.00),
(5,'AAA',0,0.00 ),
(6,'AAA',0,0.00 ),
(7,'AAA',1,140.00),
(1,'BBB',1,200.00),
(2,'BBB',0,0.00 ),
(3,'BBB',0,0.00 ),
(4,'BBB',0,0.00 ),
(5,'BBB',0,0.00 ),
(6,'BBB',0,0.00 ),
(7,'BBB',1,400.00);
WITH Groups AS(
SELECT *,
ROW_NUMBER() OVER (PARTITION BY UID ORDER BY SR) -
ROW_NUMBER() OVER (PARTITION BY UID, Flag ORDER BY SR) AS Grp
FROM #Sample)
SELECT SR, UID, Flag, Fees,
FIRST_VALUE(Fees) OVER (PARTITION BY UID, CASE Grp WHEN 0 THEN 1 ELSE Grp END ORDER BY SR)
FROM Groups
ORDER BY UID, SR;
DROP TABLE #Sample