SQL Duplicates remove - tsql

Question

I've a problem of duplicates in tsql. How can I remove?
This is my output:
id name ref
----------- ---------- --------------
1 John null
1 John RE
2 Smith null
2 Smith DOS
3 Van null
4 Sam CR
5 Bob null
Code:
SELECT DISTINCT
u.id,
u.name,
c.ref
FROM users u
LEFT JOIN con c on c.id=u.id
I would like the output to be like this:
id name ref
----------- ---------- --------------
1 John RE
2 Smith DOS
3 Van null
4 Sam CR
5 Bob null
This is just an example, I've few of them.
thanks

Answer 1

What about using MAX and GROUP BY:
SELECT
u.id,
u.name,
MAX(c.ref) as Ref
FROM users u
LEFT JOIN con c on c.id=u.id
GROUP BY
u.id,
u.name

Answer 2

Try below query, this will give you the exact required output:
DECLARE #SAMPLEDATA TABLE(id INT, name VARCHAR(100), ref VARCHAR(100))
INSERT INTO #SAMPLEDATA VALUES
(1, 'John', null),
(1, 'John', 'RE'),
(2, 'Smith', null),
(2, 'Smith', 'DOS'),
(3, 'Van', null),
(4, 'Sam', 'CR'),
(5, 'Bob', null)
;WITH SAMPLEDATA
AS
(
SELECT ROW_NUMBER()OVER (ORDER BY (SELECT 100))SNO,* FROM #SAMPLEDATA
)
SELECT ID,NAME,REF FROM(
SELECT * ,ISNULL((SELECT CASE WHEN T2.ID=T1.id AND T1.ref IS NULL THEN 'R' ELSE 'NR' END
FROM SAMPLEDATA T2 WHERE T2.SNO=T1.SNO+1),'NR')COL FROM SAMPLEDATA T1) DATA WHERE COL='NR'
OUTPUT
------------------
ID NAME REF
------------------
1 John RE
2 Smith DOS
3 Van NULL
4 Sam CR
5 Bob NULL
------------------

Answer 3

Please make use of below query:
DECLARE #TABLE TABLE
(id INT, name VARCHAR(10),ref VARCHAR(10))
INSERT INTO #TABLE VALUES
(1,'John',null),
(1,'John','RE'),
(2,'Smith',null),
(2,'Smith','DOS'),
(3,'Van',null),
(4,'Sam','CR'),
(5,'Bob',null)
SELECT id,name,ref FROM
(
SELECT
id,name,ref,RN = ROW_NUMBER() OVER (PARTITION BY id,name ORDER BY ref DESC)
FROM
#TABLE
) AS A
WHERE RN < 2
You can use this too:
SELECT
u.id,
u.name,
MAX(u.ref) as Ref
FROM
#TABLE u
GROUP BY
u.id,
u.name