On Mar 3, 2006, at 14:13 , Michael Fuhr wrote:
On Fri, Mar 03, 2006 at 04:28:01AM +0100, Andreas wrote:
How can I have a constraint, that prohibits nesting or overlapping
intervals?
1 7 2006-1-1 2006-1-31
2 9 2006-2-1 2006-2-28 OK
3 5 2006-1-10 2006-1-20 BAD lies within line 1
4 3 2006-1-20 2006-2-10 BAD starts within
line 1
and ends in line 2
This is just a brainstorm, but what about creating a composite type,
a comparison function, and an operator class, then declaring a
unique index on that composite type?
Another way is presented in Snodgrass' "Developing Time-Oriented
Database Applications in SQL", out of print but available as a PDF
download from his website:
http://www.cs.arizona.edu/people/rts/tdbbook.pdf
You'll need to use CREATE CONSTRAINT TRIGGER rather than just CREATE
TRIGGER to apply the constraints you're looking for, as often you'll
need to wrap a multi-statement update in a transaction to ensure
integrity.
Michael Glaesemann
grzm myrealbox com
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