Question

I have a simple problem , Although i believe its simple , am not able to figure out the same.

Consider i have the below table with exactly same data as given below :

CREATE TABLE #temp
    (
    link varchar(255),
    number INT,
    fname varchar(255)            
    )

    insert into #temp VALUES ('abc',1,'f1')
    insert into #temp VALUES ('abc',2,'f2')
    insert into #temp VALUES ('abc',3,'f3')
    insert into #temp VALUES ('abc',4,'f6')
    insert into #temp VALUES ('abc',10,'f100')

    insert into #temp VALUES ('abe',-1,'f0')
    insert into #temp VALUES ('abe',1,'f1')
    insert into #temp VALUES ('abe',2,'f2')
    insert into #temp VALUES ('abe',3,'f3')
    insert into #temp VALUES ('abe',4,'f6')
    insert into #temp VALUES ('abe',20,'f200')

    insert into #temp VALUES ('cbe',-1,'f0')
    insert into #temp VALUES ('cbe',1,'f1')
    insert into #temp VALUES ('cbe',2,'f2')
    insert into #temp VALUES ('cbe',3,'f3')

Now for a given link , i need to get the max ‘number’ and the corresponding ‘fname’ which has the max ‘number’ for the given ‘link’.

1)Ex : if link is ‘abc’ , output should be
abc, 10, f100

2)Ex : if link if ‘abe’ , Output should be
abe, 20, f200

3)Now link can be also given as a pattern , like (link like ‘ab%’) , so output should be

abc, 10, f100

abe, 20, f200

4)if (link like ‘cb%’) , so output should be
cbe, 3, f3

Any help in writing this group by query. I have a solution using CAST and string concat like below , but that seems to be in-efficient.

select link,number,fname from #temp 
where link like 'ab%' and link+'_'+CAST(number AS varchar(255)) 
in (select link+'_'+CAST(MAX(number) AS varchar(255)) from #temp 
group by link)

Thanks..

Answer 1

Using a self join:

SELECT x.link,
       x.number,
       x.fname
  FROM #temp x
  JOIN (SELECT t.link,
               MAX(t.number) AS max_number
          FROM #temp t
      GROUP BY t.link) y ON y.link = x.link
                        AND y.max_number = x.number

Using a CTE and ROW_NUMBER (SQL Server 2005+):

WITH cte AS (
   SELECT x.link,
          x.number,
          x.fname,
          ROW_NUMBER() OVER(PARTITION BY x.link
                                ORDER BY x.number DESC) rank
     FROM #temp x)
SELECT c.link, 
       c.number,
       c.fname
  FROM cte c
 WHERE c.rank = 1