Sql query for the following situation - sql

Question

Tom loves sports. Every month he takes rest for a while and plays his favorite sport. He changes the game during the month and its change history is shown in table.
Challenge: What is the first and last favorite sport played by Tom?
Tom Favourite Sports
----------------------
Month PreviousSport CurrentSport
JAN REST CRICKET
JAN CRICKET RUGBY
JAN RUGBY VOLLEYBALL
JAN VOLLEYBALL FOOTBALL
JAN FOOTBALL TENNIS
JAN TENNIS RUGBY
FEB REST KAYAKING
FEB KAYAKING SNOWBOARDING
FEB SNOWBOARDING SKATING
FEB SKATING RAFTING
FEB RAFTING KAYAKING
MAR REST RACING
MAR RACING GLIDING
MAR GLIDING SKYDIVING
And the output should be
Month FirstSport LastSport
JAN CRICKET RUGBY
FEB KAYAKING KAYAKING
MAR RACING SKYDIVING
CHANGE : Slight modification to the source table
MTH PREVIOUS_SPORT CURRENT_SPORT
JAN VOLLEYBALL FOOTBALL
FEB REST KAYAKING
MAR REST RACING
JAN CRICKET RUGBY
FEB SNOWBOARDING SKATING
MAR RACING GLIDING
JAN RUGBY VOLLEYBALL
FEB SKATING RAFTING
MAR GLIDING SKYDIVING
JAN FOOTBALL TENNIS
FEB RAFTING KAYAKING
JAN TENNIS RUGBY
JAN REST CRICKET
Now how do I get the previous output?
Thanks in advance.

Answer 1

I just have considered ID column for Table, we can avoid it & convert Jan/Feb/March as Month Numbers & go ahead without ID column. But for quick reply, This is it !!!
Select Main.[Month],F.CurrentSport,L.CurrentSport from
(
Select a.[Month],min(r) fSport ,max(r) lSport from
(select * ,ROW_NUMBER() over (Partition by Month order by ID) as R
from Tom
)a
group by a.[Month]
)as Main
inner join
(
select *, ROW_NUMBER() over (Partition by Month order by ID) as R
from Tom
)as F on F.R = Main.fSport and f.[Month] = Main.[Month]
inner join
(
select *, ROW_NUMBER() over (Partition by Month order by ID) as R
from Tom
)as L on L.R = Main.lSport and L.[Month] = Main.[Month]
order by F.ID
See Fiddle DEMO HERE
One more variant, avoiding ROW_Number multiple times & using CTE. I think this should be faster than previous.
;With CTE as
(
select ID,[Month] as M,CurrentSport as Sport
, ROW_NUMBER() over (Partition by Month order by ID) as R
from Tom
), CTE1 as
(
Select M, Min(R) as FS ,Max(R) as LS from CTE
group by M
)
Select CTE1.M,F.Sport as First,L.Sport as Last from CTE1
inner join CTE as F on F.R = CTE1.FS and F.M = CTE1.M
inner join CTE as L on L.R = CTE1.LS and L.M = CTE1.M
order by L.ID asc
See DEMO HERE

Answer 2

I don't think we need the ID column as such. We can work with RowNumber.
So it should be coming up like this :
SELECT Mintmp.mnth,
Mintmp.currentsport AS FirstSport,
MaxTmp.currentsport AS CurrentSport
FROM (SELECT Row_number()
OVER(
partition BY mnth
ORDER BY mnth) AS RowNum,
*
FROM #T1) MinTmp
INNER JOIN (SELECT Min(rownum) AS MinRow,
mnth,
Max(rownum) AS MaxRow
FROM (SELECT Row_number()
OVER(
partition BY mnth
ORDER BY mnth) AS RowNum,
*
FROM #T1) tmp
GROUP BY mnth) grpTable
ON grpTable.minrow = MinTmp.rownum
AND grpTable.mnth = MinTmp.mnth
INNER JOIN (SELECT Row_number()
OVER(
partition BY mnth
ORDER BY mnth) AS RowNum,
*
FROM #T1) MaxTmp
ON Maxtmp.rownum = grpTable.maxrow
AND Maxtmp.mnth = grpTable.mnth