Date:         Thu, 6 Jan 2011 17:44:32 -0500
Reply-To:     Chang Chung <chang_y_chung@HOTMAIL.COM>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Chang Chung <chang_y_chung@HOTMAIL.COM>
Subject:      finding gaps given date ranges and covered date ranges

Saw this interesting question posted on somewhere else:
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I have two sets of data with different date ranges.
Tbl 1:
ID, Date_Start, Date_End
1, 2010-01-01, 2010-01-09
1, 2010-01-10, 2010-01-19
1, 2010-01-30, 2010-01-31

Tbl 2:
ID, Date_Start, Date_End
1, 2010-01-01, 2010-01-04
1, 2010-01-08, 2010-01-17
1, 2010-01-30, 2010-01-31

I'd like to find cases date ranges do not entirely overlap date ranges in
Tbl 2. So for instance, in this example, I'd like output that looks
something like this --
Output:
ID, Gap_Start, Gap_End
1, 2010-01-05, 2010-01-07
1, 2010-01-18, 2010-01-19

Date ranges will never overlap within a table. To do this, I'm using either
SQL or SAS. Unfortunately, the datasets are big enough (millions of
records) that I can't just brute force it.
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