Path: utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!uunet!cimshop!davidm From: cimshop!davidm@uunet.UU.NET (David S. Masterson) Newsgroups: comp.databases Subject: Re: outerjoins Message-ID: Date: 15 Aug 90 23:51:46 GMT References: <28462@netnews.upenn.edu> Sender: davidm@cimshop.UUCP Organization: Consilium Inc., Mountain View, California. Lines: 30 In-reply-to: aaron@grad2.cis.upenn.edu's message of 14 Aug 90 13:59:45 GMT In article <28462@netnews.upenn.edu> aaron@grad2.cis.upenn.edu (Aaron Watters) writes: The various varieties of outerjoins are interesting operations. In particular, they are interesting because they don't act like relational operations in the sense that (r outerjoin s) minus t or (r outerjoin s) join t don't seem to be well defined. To be fanciful, I would hypothesize that the outerjoin lies on the fringes of the standard relational paradigm, and its usefulness indicates useful directions in which the paradigm should be broadened. Comments? Read Codd's new book on RMV2 before saying that outer-joins are on the fringes of the relational model. The outer join also goes far beyond just the outer equijoin to include all operators (<, >, !=, etc). What are interesting (simple) examples of the uses for outerjoins? When dealing with object-orientation in a relational database, normalization of the database may tend to break up an object into several tables. Not all of these tables may be filled in for an object. Trying to put the object back together at any point in time will be best done with an outer equijoin (based on the key of the object). -- ==================================================================== David Masterson Consilium, Inc. uunet!cimshop!davidm Mtn. View, CA 94043 ==================================================================== "If someone thinks they know what I said, then I didn't say it!"