Can DECODE do this?

Greetings:

I'm hoping someone can share their knowledge of DECODE with me. I've used it for fairly simple purposes and it has worked well, but the current problem has be stumped.

Here's what I'd like to do...

I have a view of patient enrollment information that has 2 date fields I want to use to calculate the number of days the patient was enrolled in a given plan. The enrollment table has 2 dates, enroll_date(the date the patient enrolled) and term_date(the date the patient left the plan). I want to supply 2 more date fields, which are the beginning(begin_date) and ending(end_date) dates of the reporting period, and calculate how many member days the plan had for the reporting period.

In procedural code, I'd write something like

	if enroll_date<begin_date and term_date>end_date
	then total_days=end_date - start_date

	else if enroll_date < begin_date and term_date < end_date
	then total_days=term_date - start_date

	else if enroll_date > begin_date and term_date > end_date
	then total_days=end_date - enroll_date

	else if enroll_date > begin_date and term_date < end_date
	then total_days=term_date - enroll_date
	

Now, how can I do something like this using DECODE? Any ideas appreciated. I've looked at several examples but can't find any where the ifs contain an "AND" clause.

Thanks for your help!

John Dunn
The University Physicians Received on Thu Aug 22 1996 - 00:00:00 CEST