SQL Case Statement with Subqueries - sql

Question

I am trying to write a query to report on how many times a part was used during a specific month. For example, take February as the reporting month. If P1 was installed on A1 until 2014-02-05 and was used within 2014-02-01 to 2014-02-05 then I would need to Sum that up. Also if P1 was installed on A2 then I would need to sum up the usage up to 2014-02-28.
| part | date_trans | transaction | unit |
---------------------------------------------
p1 2014-02-05 removed A1
p1 2014-02-07 installed A2
| unit | daily usage | date |
A1 3 2014-02-01
A1 2 2014-02-03
A2 2 2014-02-05
A2 4 2014-02-08
A2 2 2014-02-20
Notice for the record
| unit | daily usage | date |
A2 2 2014-02-05
We do not need to take account because P1 was not installed on A2 on 2014-02-05.
Here is my attempt so far..
SELECT
CASE
WHEN h.date_trans between '2014-01-31' and '2014-02-28' and transaction='removed' THEN...
END AS 'test'
FROM history h join acu on(acu.unit=h.unit)
WHERE h.part='P1'

Answer 1

You can try the following query, using CTE's:
with history_installed as
(select part,
case
when date_trans <= '2014-02-01' then '2014-02-01'
else date_trans
end date_trans
from history
where transaction = 'installed' and date_trans < '2014-03-01')
, history_removed as
(select part,
case
when date_trans >= '2014-02-28' then '2014-02-28'
else date_trans
end date_trans
from history
where transaction = 'removed' and date_trans >= '2014-02-01')
select acu.*
from acu
inner join history_installed on history_installed.date_trans <= acu.date
inner join history_removed on history_removed.date_trans >= acu.date

Answer 2

Something like this.
/*
create table #t1 (part char(2), date_trans date, trans char(10), unit char(2))
go
insert #t1 values
('p1', '2014-02-05', 'removed' , 'A1'),
('p1', '2014-02-07' , 'installed', 'A2')
go
create table #t2 (unit char(2), usage int, dt date)
go
insert #t2 values
( 'A1', 3, '2014-02-01'),
( 'A1', 2, '2014-02-03'),
( 'A2', 2, '2014-02-05'),
( 'A2', 4, '2014-02-08'),
( 'A2', 2, '2014-02-20')
*/
declare #min date = '20140201', #max date = '20140228'
;with x as (
select *,
isnull(case trans when 'removed' then lag(date_trans) over(partition by part order by date_trans) else date_trans end, #min) as date_start,
isnull(case trans when 'installed' then lead(date_trans) over(partition by part order by date_trans) else date_trans end, #max) as date_end
from #t1
)
select #t2.unit, x.part, sum(#t2.usage)
from #t2
inner join x on #t2.dt between x.date_start and x.date_end
and x.unit = #t2.unit
group by #t2.unit, x.part
-- drop table #t1, #t2
Here's the query for the older (pre-2012) versions:
;with x as (
select *, row_number() over(partition by part order by date_trans) as rn
from #t1
),
y as (
select x1.*,
case x1.trans when 'removed' then isnull(x2.date_trans, #min) else x1.date_trans end as date_start,
case x1.trans when 'installed' then isnull(x3.date_trans, #max) else x1.date_trans end as date_end
from x x1
left outer join x x2 on x1.rn = x2.rn+1
left outer join x x3 on x1.rn = x3.rn-1
)
select #t2.unit, y.part, sum(#t2.usage)
from #t2
inner join y on #t2.dt between y.date_start and y.date_end
and y.unit = #t2.unit
group by #t2.unit, y.part