Grouping by an aggregate column - sql

Question

I have a requirement to show a listing of data associated with a given widget, however I can only aggregate on the widget while it's in sequence (essentially breaking the running total when the widget changes).
Here's a bit of a break down of what I mean...
Example data:
ID WIDGET PART
1 A000 B22
2 A000 B23
3 A002 B24
4 A001 B25
5 A001 B26
6 A000 B27
Desired output:
WIDGET MINPART COUNT
A000 B22 2
A002 B24 1
A001 B25 2
A000 B27 1
In SQL Server I've tried running the following:
with a as (
select
WIDGET,
min(PART) over (partition by WIDGET) as MINPART,
1 tcount
from test )
select WIDGET, MINPART, sum(tcount)
from a
group by WIDGET, MINPART
But this just results in the usual aggregation you might expect. I.E.:
WIDGET MINPART COUNT
A000 B22 3
A002 B24 1
A001 B25 2

Answer 1

Does this work for you?
;with x as (
select *,
lag(widget) over(order by id) as lg
from #t
),
y as (
select *, sum(case when widget<>lg then 1 else 0 end) over(order by id) as grp
from x
)
select widget, min(part), count(*)
from y
group by widget, grp

Answer 2

Don't you mean to use the named columns?, i.e.
with a as (
select
WIDGET,
min(PART) over (partition by WIDGET) as MINPART,
1 tcount
from Widget )
select WIDGET, MINPART, sum(tcount)
from a
group by Widget, MinPart;
SqlFiddle here

Answer 3

we can write this one using derived table also other way
DECLARE #Widget TABLE
(ID INT,
Widget NVARCHAR(10),
PART NVARCHAR(10));
INSERT INTO #Widget VALUES
(1, 'A000', 'B22'),
(2, 'A000', 'B23'),
(3, 'A002', 'B24'),
(4, 'A001', 'B25'),
(5, 'A001', 'B26'),
(6, 'A000', 'B27');
IF OBJECT_ID('tempdb..#t1') IS NOT NULL
DROP TABLE #t1
select Widget,PART,1 as t into #t1 from
(select Widget,MIN(PART)OVER (PARTITION BY Widget) As Part from #Widget
GROUP BY Widget,ID,PART)AS F
select Widget,PART,SUM(t) from #t1
group by Widget, Part

Answer 4

#dean solution is neat but a pure SQLServer 2008 solution is possible, the idea is the same, the ranker formula
sum(case when widget<>lg then 1 else 0 end) over(order by id) as grp
can be faked by a running total, for the record the full query is
WITH part AS (
SELECT a.id, a.widget, a.part
, breaker = CASE WHEN a.widget<>coalesce(b.widget, a.widget)
THEN 1
ELSE 0
END
FROM Widgets a
LEFT JOIN Widgets b ON a.id = b.id + 1
)
, DATA AS(
SELECT a.id, a.widget, a.part
, rank = (SELECT sum(breaker) FROM part b WHERE a.id >= b.id)
FROM part a
)
SELECT widget
, minpart = min(part)
, [count] = count(1)
FROM DATA
GROUP BY widget, rank