generate new column using other columns - tsql

Question

I am stuck with generating a new column. The table has three columns(C_ID, C_rank, Date).
C_ID C_ Rank NewColumn(Cycle) Date
42 A 1 October 14, 2010
42 B 1 October 26, 2010
42 A 2 February 16, 2011
43 A 1 December 17, 2010
44 A 1 July 28, 2010
44 B 1 August 10, 2010
44 A 2 January 11, 2011
44 B 2 January 28, 2011
45 A 1 July 30, 2010
45 B 1 August 9, 2010
45 B 1 September 24, 2010
45 A 2 April 5, 2011
45 B 2 April 26, 2011
I want to generate one more column called Cycle in such a way that for each C_ID, it should generate the number start from one and increment the number from next C_rank = 'A' (a shown above).
I tried using row_number, but no luck.
Maybe some loop option till next C_Rank = 'A' works.
How can this be done?

Answer 1

You should be able to get this done using ROW_NUMBER() and PARTITION BY
;WITH YourDataCTE AS
(
SELECT
C_ID, C_Rank, Date,
ROW_NUMBER() OVER(PARTITION BY C_ID,C_Rank ORDER BY Date DESC) AS 'Cycle'
FROM
dbo.YourTable
)
SELECT *
FROM YourDataCTE
Does that do what you're looking for??
The PARTITION BY C_ID,C_Rank will cause the ROW_NUMBER to start at 1 again for each different value of C_ID,C_Rank - I didn't know what ORDER BY clause within a single partition (a single value of C_ID,C_Rank) you're looking for and just guessed it might be Date DESC (newest date first).

Answer 2

You could count the number of previous A's in a subquery:
select *
, (
select count(*)
from #YourTable yt2
where yt2.C_ID = yt1.C_ID
and yt2.C_Rank = 'A'
and yt2.Date <= yt1.Date
) as Cycle
from #YourTable yt1
order by
C_ID, Date
Example at ODATA.

Answer 3

Do a self join for all records with the same C_ID, a previous date, and a C_Rank='A' and count them.
select t1.C_ID, t1.C_Rank, count(t2.C_Rank) Cycle, t1.Date
from MyTable t1
left join MyTable t2 on t1.C_ID=t2.C_ID
and t2.Date<=t1.Date
and t2.C_Rank='A'
group by t1.C_ID, t1.C_Rank, t1.Date
order by t1.C_ID, t1.Date

Answer 4

Below code fulfill the requirement:
create table #Temp_Table
(
C_ID int
, C_Rank char(1)
, Date datetime
, NewColumn int
)
insert into #Temp_Table
(
C_ID
, C_Rank
, Date
)
select 42, ‘A’, ’10/14/2010′
union all
select 42, ‘B’, ’10/26/2010′
union all
select 42, ‘B’, ’10/14/2010′
union all
select 42, ‘C’, ’10/26/2010′
union all
select 42, ‘A’,’02/16/2011′
union all
select 43, ‘A’, ’12/17/2010′
union all
select 44, ‘A’, ’07/28/2010′
union all
select 44, ‘B’, ’08/10/2010′
union all
select 44, ‘A’, ’01/11/2011′
union all
select 44, ‘B’, ’01/28/2011′
union all
select 44, ‘C’, ’10/14/2010′
union all
select 44, ‘D’, ’10/26/2010′
Select ‘Original Data’ Comment
,*
from #Temp_Table
/*
This would be Actual Script to get the New ID based on information you provided
*/
Declare #Count int
,#C_ID int
,#C_Rank char(1)
,#total_Count int
,#Count_Partition int
,#Previous_ID int
Declare #Table Table (ID int IDENTITY(1,1), C_ID int, C_Rank char(1), Date datetime, NewColumn int )
Set #Count = 1
Set #Count_Partition = 0
insert into #Table
Select *
from #Temp_Table
Select #total_Count = ISNULL(MAX(ID),0)
from #Table
While #Count < = #total_Count
Begin
Select #C_ID = C_ID
,#C_Rank = C_Rank
From #Table
Where ID = #Count
If #Count = 1
Set #Previous_ID = #C_ID
If #Previous_ID != #C_ID
Set #Count_Partition = 1
Else If #C_Rank = 'A'
Set #Count_Partition = #Count_Partition + 1
update #Table
Set NewColumn = #Count_Partition
Where ID = #Count
Set #Previous_ID = #C_ID
Set #Count = #Count + 1
End
Select C_ID
, C_Rank
, [Date]
, NewColumn
from #Table
–Drop table #Temp_Table