Getting the minimum of column on the basis of other field - sql

Question

I have a scenario wherein I have
Id|rank| date
1 | 7 |07/08/2015
1 | 7 |09/08/2015
1 | 8 |16/08/2015
1 | 8 |17/08/2015
1 | 7 |19/08/2015
1 | 7 |15/08/2015
2 | 7 |01/08/2015
2 | 7 |02/08/2015
2 | 8 |16/08/2015
2 | 8 |17/08/2015
2 | 7 |26/08/2015
2 | 7 |28/08/2015
My desired solution is
1 | 7 |07/08/2015
1 | 8 |16/08/2015
1 | 7 |15/08/2015
2 | 7 |01/08/2015
2 | 8 |16/08/2015
2 | 7 |26/08/2015
i.e for each block of id and rank I want the minimum of date.
I have tried using while loop as there are thousands of records it is taking 2 hours to load.Is there any other way to do please suggest.

Answer 1

For each row give unique row number using necessary order. (As I get Id is more important than date and date is more important than rank).
Join resulting table to itself using row numbers shifted by one row (d1.RowNum = d2.RowNum+1).
Select only rows that are joined to "other block" rows (d1.Id <> d2.Id or d1.Rank <> d2.rank).
Depending on shifting direction and selected table either maximal or minimal date will be selected.
Don't forget "edge case" - row that due to shifting can't be joined (that's why not inner join and d1.RowNum = 1 condition used).
;WITH dataWithRowNums as (
select Id, Rank, Date,
RowNum = ROW_NUMBER() OVER (ORDER BY Id,date,rank)
from YourTable
)
select d1.Id, d1.Rank, d1.Date
from dataWithRowNums d1
left join dataWithRowNums d2
on d1.RowNum = d2.RowNum+1 and (d1.Id <> d2.Id or d1.Rank <> d2.rank)
where not d2.Id is null or d1.RowNum = 1
This code returns result bit different from yours:
Id Rank Date
1 7 2015-08-07
1 8 2015-08-16
1 7 2015-08-19 <-- you've got here 2015-08-15
2 7 2015-08-01
2 8 2015-08-16
2 7 2015-08-26
As block (Rank 8 Id 1) have started at 16/08 so row 15/08 for rank 7 is related to first block (rank7 Id1).
If you still need your sorting (so 15/08 rank 7 is related to second block (rank7 id1)) then you should provide your own RowSorting data and then ask here about another solution for another task )

Answer 2

Here is the query using row_number()
;WITH cte_rec
as (SELECT Id,Rank,Date
,ROW_NUMBER()OVER (partition by Id,Rank ORDER BY date) as RNO
FROM YourTable)
SELECT Id,Rank,Date
FROM cte_rec
WHERE RNO =1

Answer 3

This is what I have tried and is running as expected
create table #temp
(
iden int identity(1,1),
ID int,
[rank] int,
[date] date,
dr_id int,
rownum_id int,
grouprecord int
)
Insert into #temp(id,rank,date)
select 1 , 7 ,'07/08/2015'
union all select 1 , 7 ,'09/08/2015'
union all select 1 , 8 ,'08/16/2015'
union all select 1 , 8 ,'08/17/2015'
union all select 1 , 7 ,'08/19/2015'
union all select 1 , 7 ,'08/15/2015'
union all select 2 , 7 ,'08/01/2015'
union all select 2 , 7 ,'08/02/2015'
union all select 2 , 8 ,'08/16/2015'
union all select 2 , 8 ,'08/17/2015'
union all select 2 , 7 ,'08/26/2015'
union all select 2 , 7 ,'08/28/2015'
update t1
set dr_id = t2.rn
from #temp t1 inner join
(select iden, dense_rank() over(order by id) as rn from #temp) t2
on t1.iden = t2.iden
update t1
set rownum_id = t2.rn
from #temp t1 inner join
(select iden, row_number() over(partition by dr_id order by id) as rn from #temp) t2
on t1.iden = t2.iden
select *,row_number() over(order by iden)rn into #temp1 from
(
select t2.*
from #temp t1 inner join #temp t2
on (t1.dr_id = t2.dr_id or t2.dr_id = (t1.dr_id +1) ) and ( t1.rank<>t2.rank or t2.dr_id = (t1.dr_id +1) )
and t2.iden = t1.iden + 1
)a
declare #id int,#miniden int,#maxiden int,#maxid int
set #id = 1
select #maxid = max(iden) from #temp
while exists(select 1 from #temp1 where rn = #id)
begin
Select #miniden = iden from #temp1
where rn = #id
Select #maxiden = iden from #temp1
where rn = #id+1
update #temp
set grouprecord = #id +1
where iden between #miniden and #maxiden
IF(#maxiden IS NULL)
BEGIN
Update #temp
set grouprecord = #id +1
where iden between #miniden and #maxid
END
set #id = #id + 1
SET #miniden =NULL
SET #maxiden = NULL
end
UPDATE #TEMP
SET GROUPRECORD = 1
WHERE GROUPRECORD IS NULL
select min(date) as mindate,grouprecord from #temp
group by grouprecord
Thanks everyone the help :)