T-SQL query to obtain the no of days an item was at the current price - sql

Question

Declare #sec_temp table
(
sec_no varchar(10),
amount money,
price_date date
)
insert #sec_temp
values
('123ABC', 25, '2011-01-20'),
('123ABC', 25, '2011-01-19'),
('123ABC', 25, '2011-01-18'),
('123ABC', 20, '2011-01-15'),
('123ABC', 22, '2011-01-13'),
('456DEF', 22, '2011-01-13')
Problem: To list out the distinct sec_no with the latest price (amount) and the number of days it was at the current price. In this case,
Result:
sec_no amount no_of_days_at_price
123ABC 25 3 e.g. 01-18 to 01-20
456DEF 22 1 e.g. 01-13

Answer 1

select
a.sec_no,
a.amount,
min(price_date) as FirstDateAtPrice,
No_of_days_at_price = COALESCE(DATEDIFF(d, c.price_date, a.price_date),0)
from (
select *, ROW_NUMBER() over (partition by sec_no order by price_date desc) rn
from #sec_temp) a
outer apply (
select top 1 *
from #sec_temp b
where a.sec_no=b.sec_no and a.amount <> b.amount
order by b.price_date desc
) c
where a.rn=1
The subquery A works out the greatest-1-per-group, which is to say the most recent price record for each sec_no. The subquery C finds the first prior record that holds a different price for the same sec_no. The difference in the two dates is the number of days sought. If you need it to be one for no prior date, change the end of the COALESCE line to 1 instead of 0.
EDITED for clarified question
To start counting from the first date equal to the current rate, use this query instead
select
sec_no,
amount,
No_of_days_at_price = 1 + DATEDIFF(d, min(price_date), max(price_date))
from (
select *,
ROW_NUMBER() over (partition by sec_no order by price_date desc) rn,
ROW_NUMBER() over (partition by sec_no, amount order by price_date desc) rn2
from #sec_temp
) X
WHERE rn=rn2
group by sec_no, amount
AND FINALLY If the required result is actually the days between
the first date on which the price is equal to current; and
today
Then the only part to change is this:
No_of_days_at_price = 1 + DATEDIFF(d, min(price_date), getdate())

Answer 2

Here's one approach, first looking up the latest price, and then the last price that was different:
select secs.sec_no
, latest.amount as price
, case when previous.price_date is null then 1
else datediff(day, previous.price_date, latest.price_date)
end as days_at_price
from (
select distinct sec_no
from #sec_temp
) secs
cross apply
(
select top 1 amount
, price_date
from #sec_temp
where sec_no = secs.sec_no
order by
price_date desc
) latest
outer apply
(
select top 1 price_date
from #sec_temp
where sec_no = secs.sec_no
and amount <> latest.amount
order by
price_date desc
) previous
This prints:
sec_no price days_at_price
123ABC 25,00 5
456DEF 22,00 1