How can i select some row from multiple row in the same group of data

Question

I want to select some row from multiple row in the same group of data.
ColumnA        
Column B
1                  OK
1                   NG
2                   NG
2                          NG
3                          OK
3                          OK
I want the row of group of
ColumnA if  ColumnB contain even 'NG'
row , select only one row which  Column B = 'NG'
the result i want = 
ColumnA         Column B
1                         NG
2                   NG
3                          OK
Thank you

Answer 1

That's some awful explanation, but I think this is what you were driving at:
DECLARE @forumTable TABLE (a INT, b CHAR(2))
INSERT INTO @forumTable (a, b)
VALUES
(1, 'OK'),(1, 'NG'),
(2, 'NG'),(2, 'NG'),
(3, 'OK'),(3, 'OK')
SELECT f.a, MIN(COALESCE(f2.b,f.b)) AS b
FROM @forumTable f
LEFT OUTER JOIN @forumTable f2
ON f.a = f2.a
AND f.b <> f2.b
GROUP BY f.a