Distinct Value of a column in sql server 2008

Question

Hello all I have made a query using left outer joins which result in some what like the table below:

| 00-00-00-00-00 | 1 | a.txt |
| 00-00-00-00-00 | 2 | b.txt |
| 00-00-00-00-00 | 1 | c.txt |
| 11-11-11-11-11 | 2 | d.txt |

What I want is Distict value of the MAC Column below is the SQL Fiddle to understand better.

SQLFIDDLE

Thanks

EDIT

The purpose is that 2 and 3 are useless or redundant data where as 1 and 4 are useful means the 1 and 4 show the current file on the MACs

Output:

| 00-00-00-00-00 | 1 | a.txt |
| 11-11-11-11-11 | 2 | d.txt |

Answer 1

Is not possible to answer exactly what you ask. However, usually folk that express the question you ask really mean to ask something like 'I want all the columns for a sample of rows containing only distinct MacAddress values'. This question has many answers, as the result is non-deterministic. A trivial solution is to pick the first (for whatever definition of 'first') row for each MacAddress:

with cte as (
  select row_number() over (partition by MacAddress order by CounterNo) as rn, *
             from Heartbeats
  )
select * from cte where rn = 1;

Answer 2

If you want to get only the distinct macaddresses, you can do:

SELECT DISTINCT macaddress FROM heartbeats

If you want all the columns alongside the distinct macaddress, you need to create a rule to get them. The query below gives you the ones with the highest id for each macaddress:

SELECT t1.*
FROM heartbeats t1
LEFT JOIN heartbeats t2
    ON (t1.macaddress = t2.macaddress AND t1.id < t2.id)
WHERE t2.id IS NULL

sqlfiddle demo

EDIT:

Since in original query the code used doesnt have ID column the above query was refined as:

with cte as (
select ROW_NUMBER() OVER(ORDER BY (Select 0)) AS ID,* from heartBeats
)


SELECT t1.*
FROM cte t1
LEFT JOIN cte t2
    ON (t1.macaddress = t2.macaddress AND t1.id < t2.id)
WHERE t2.id IS NULL

SQL Fiddle

Answer 3

SELECT hb1.* FROM [heartbeats] as hb1
       LEFT OUTER JOIN [heartbeats] as hb2   
       ON (hb1.macaddress = hb2.macaddress AND hb1.id > hb2.id) 
         WHERE hb2.id IS NULL;

Answer 4

You have to neglect the file name. See http://sqlfiddle.com/#!3/a75e47/13