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difference between UNION operator and OR in where clause

From: Mike <gongweigang_at_gmail.com>
Date: Tue, 10 Jul 2007 06:39:30 -0700
Message-ID: <1184074770.394660.52860_at_d55g2000hsg.googlegroups.com> 





tables:

1. publication(pubid, title)
2. book(pubid, date)
3. journal(pubid, date)





purpose: find all publication titles for books or journals.



solution 1: use set "union"



select title


from publication, ( (select pubid from book) UNION (select pubid from
journal)) bj


where publication.pubid = bj.pubid




solution 2: use "or" operator in the where clause



select title


from publication, book, journal


where publication.pubid = book.pubid or publication.pubid =
journal.pubid




This example is taken from some lecture notes about sql. The notes
said the solution 2 was wrong.



Anyone knows why ?



Thanks ahead.
Received on Tue Jul 10 2007 - 15:39:30 CEST












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