SQL Question: Getting Datediff in days elapsed for each record in a group - sql

Question

Given this table:
How can I get the datediff in days between each status_date for each group of ID_Number? In other words I need to find the number of elapsed days for each status that the ID_Number has been given.
Some things to know:
All ID_Number will have a received_date which should be the earliest date for each ID_Number (but app doesn't enforce)
For each ID_Number there will be a status with a corresponding status_date which is the date that the ID_Number was given that particular status.
The status column doesn't always necessarily go in the same order every time (app doesn't enforce)
All ID_Number will have a closed_date which should be the latest date (but app doesn't enforce)
Sample output:
So for ID_Number 2001, the first date (received_date) is 2009-05-02 and the next date you encounter has a status of 'open' and is 2009-05-02 so elapsed days is 0. Moving on to the next date encountered is 2009-05-10 with a status of 'invest' and the elapsed days is 8 counting from the prior date. The next date encountered is 2009-07-11 and the elapsed days is 62 counting from the previous date.
Edited to add:
Is it possible to have the elapsed days end up as a column on this table/view?
I also forgot to add that this is SQL Server 2000.

Answer 1

What I understand is that you need the difference between the first status_date and the next status_date for the same id and so on up to the closed_date.
This will only work in SQL 2005 and up.
;with test as (
select
key,
id_number,
status,
received_date,
status_date,
closed_date,
row_number() over (partition by id order by status_date, key ) as rownum
from #test
)
select
t1.key,
t1.id_number,
t1.status,
t1.status_date,
t1.received_date,
t1.closed_date,
datediff(d, case when t1.rownum = 1
then t1.received_date
else
case when t2.status_date is null
then t1.closed_date
else t2.status_date
end
end,
t1.status_date
) as days
from test t1
left outer join test t2
on t1.id = t2.id
and t2.rownum = t1.rownum - 1
This solution will work with SQL 2000 but I am not sure how good will perform:
select *,
datediff(d,
case when prev_date is null
then closed_date
else prev_date
end,
status_date )
from (
select *,
isnull( ( select top 1 t2.status_date
from #test t2
where t1.id_number = t2.id_number
and t2.status_date < t1.status_date
order by t2.status_date desc
),received_date) as prev_date
from #test t1
) a
order by id_number, status_date
Note: Replace the #Test table with the name of your table.

Answer 2

Some sample output would really help, but this is a guess at what you mean, assuming you want that information for each ID_Number/Status combination:
select ID_Number, Status, EndDate - StartDate as DaysElapsed
from (
select ID_Number, Status, min(coalesce(received_date, status_date)) as StartDate, max(coalesce(closed_date, status_date)) as EndDate
from Table1
group by ID_Number, Status
) a

Answer 3

The tricky bit is determining the previous status and putting it on the same row as the current status. It would be simplified a little if there were a correlation between Key and StatusDate (i.e. that Key(x) > Key(y) always implies StatusDate(x) >= StatusDate(y)). Unfortunately, that doesn't seem to be the case.
PS: I am assuming Key is a unique identifier on your table; you haven't said anything to indicate otherwise.
SELECT Key,
ID_Number,
(
SELECT TOP 1 Key
FROM StatusUpdates prev
WHERE (prev.ID_Number = cur.ID_Number)
AND ( (prev.StatusDate < cur.StatusDate)
OR ( prev.StatusDate = cur.StatusDate
AND prev.Key < cur.Key
)
)
ORDER BY StatusDate, Key /*Consider index on (ID_Number, StatusDate, Key)*/
) PrevKey
FROM StatusUpdates cur
Once you have this as a basis, it's easy to extrapolate to any other info you need from the current or previous StatusUpdate. E.g.
SELECT c.*,
p.Status AS PrevStatus,
p.StatusDate AS PrevStatusDate,
DATEDIFF(d, c.StatusDate, p.StatusDate) AS DaysElapsed
FROM (
SELECT Key,
ID_Number,
Status,
SattusDate,
(
SELECT TOP 1 Key
FROM StatusUpdates prev
WHERE (prev.ID_Number = cur.ID_Number)
AND ( (prev.StatusDate < cur.StatusDate)
OR ( prev.StatusDate = cur.StatusDate
AND prev.Key < cur.Key
)
)
ORDER BY StatusDate, Key
) PrevKey
FROM StatusUpdates cur
) c
JOIN StatusUpdates p ON
p.Key = c.PrevKey