Combining 2 tables with date ranges

SQL Apprentice Question
I'm trying to generate a report for an old database and I'm
having trouble coming up with an elegant way of going about it. Using
cursors and other 'ugly' tools I could get the job done but 1) I don't
want the report to take ages to run, 2) I'm not a big fan of cursors!

Basically there are tables that track history and each table tends to
track only a specific value housed within a date range. I'm trying to
combine the tables to get a snap-shot of the complete history. I'm
having problems dealing with the Start/End Dates from the two tables
and building the dates in the final table to be broken down by 'history
type'.


Here are a few sample records and the results I'm trying to achieve:


Table 1:
CAgyHist (ProdID,AgyID,StartDate,EndDate)
1 1 Jan 1, 2006 Jan 5, 2006
1 2 Jan 5, 2006 Jan 25, 2006
1 1 Jan 25, 2006 NULL


Table 2:
CInvHist (ProdID, InvID,StartDate,EndDate)
1 1 Jan 1, 2006 Jan 23, 2006
1 2 Jan 23, 2006 Jan 15, 2006
1 1 Jan 15, 2006 NULL


Desired End Result:
CTotalHist (ProdID,AgyID,InvID,StartDate,EndDate)
1 1 1 Jan 1, 2006 Jan 5, 2006
1 2 1 Jan 5, 2006 Jan 15, 2006
1 2 2 Jan 15, 2006 Jan 23, 2006
1 2 1 Jan 23, 2006 Jan 25, 2006
1 1 1 Jan 25, 2006 NULL


My challenge thus far has been dealing with the dates as they don't
necessarily correspond - from one table to the other.


I am by no means a database expert of any level and any help would be
greatly appreciated.



Celko Answers
Your sample data is a mess, but the usual way is to build a calendar
and join these improperly designed tables together with BETWEEN
predicates, something like:

SELECT C.cal_date, T1.a, T2.b, ..
FROM Calendar AS C, T1, T2
WHERE C.cal_date BETWEEN T1.start_date AND T1.end_date
AND C.cal_date BETWEEN T2.start_date AND T2.end_date
AND .. ;


MIssing or reversed data will not be shown in this query.