To club the rows for week days - sql

Question

I have data like below:
StartDate EndDate Duration
----------
41890 41892 3
41898 41900 3
41906 41907 2
41910 41910 1
StartDate and EndDate are respective ID values for any dates from calendar. I want to calculate the sum of duration for consecutive days. Here I want to include the days which are weekends. E.g. in the above data, let's say 41908 and 41909 are weekends, then my required result set should look like below.
I already have another proc that can return me the next working day, i.e. if I pass 41907 or 41908 or 41909 as DateID in that proc, it will return 41910 as the next working day. Basically I want to check if the DateID returned by my proc when I pass the above EndDateID is same as the next StartDateID from above data, then both the rows should be clubbed. Below is the data I want to get.
ID StartDate EndDate Duration
----------
278457 41890 41892 3
278457 41898 41900 3
278457 41906 41910 3
Please let me know in case the requirement is not clear, I can explain further.
My Date Table is like below:
DateId Date Day
----------
41906 09-04-2014 Thursday
41907 09-05-2014 Friday
41908 09-06-2014 Saturdat
41909 09-07-2014 Sunday
41910 09-08-2014 Monday
Here is the SQL Code for setup:
CREATE TABLE Table1
(
StartDate INT,
EndDate INT,
LeaveDuration INT
)
INSERT INTO Table1
VALUES(41890, 41892, 3),
(41898, 41900, 3),
(41906, 41907, 3),
(41910, 41910, 1)
CREATE TABLE DateTable
(
DateID INT,
Date DATETIME,
Day VARCHAR(20)
)
INSERT INTO DateTable
VALUES(41907, '09-05-2014', 'Friday'),
(41908, '09-06-2014', 'Saturday'),
(41909, '09-07-2014', 'Sunday'),
(41910, '09-08-2014', 'Monday'),
(41911, '09-09-2014', 'Tuesday')

Answer 1

This is rather complicated. Here is an approach using window functions.
First, use the date table to enumerate the dates without weekends (you can also take out holidays if you want). Then, expand the periods into one day per row, by using a non-equijoin.
You can then use a trick to identify sequential days. This trick is to generate a sequential number for each id and subtract it from the sequential number for the dates. This is a constant for sequential days. The final step is simply an aggregation.
The resulting query is something like this:
with d as (
select d.*, row_number() over (order by date) as seqnum
from dates d
where day not in ('Saturday', 'Sunday')
)
select t.id, min(t.date) as startdate, max(t.date) as enddate, sum(duration)
from (select t.*, ds.seqnum, ds.date,
(d.seqnum - row_number() over (partition by id order by ds.date) ) as grp
from table t join
d ds
on ds.date between t.startdate and t.enddate
) t
group by t.id, grp;
EDIT:
The following is the version on this SQL Fiddle:
with d as (
select d.*, row_number() over (order by date) as seqnum
from datetable d
where day not in ('Saturday', 'Sunday')
)
select t.id, min(t.date) as startdate, max(t.date) as enddate, sum(duration)
from (select t.*, ds.seqnum, ds.date,
(ds.seqnum - row_number() over (partition by id order by ds.date) ) as grp
from (select t.*, 'abc' as id from table1 t) t join
d ds
on ds.dateid between t.startdate and t.enddate
) t
group by grp;
I believe this is working, but the date table doesn't have all the dates in it.