Structured Query Language (SQL) - Design and Use of Relational Databases in Chemistry - page 30

union and exclude operations and the other using and , or , and not
where clauses—that yield the same result. One or other of the two state-
ments may be preferred for speed of execution, clarity of expression, or ease
of extensibility.
References
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cations: dbSwitch™: Towards a database utility. In Proceedings of the 2004
ACM SIGMOD International Conference on Management of Data SIGMOD,
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Machinery, pp. 892-896.
2. PostgreSQL 8.2 documentation. 2008. Dblink. http://www.postgresql.org/
docs/current/static/dblink.html (accessed April 21, 2008).