Anzeige
Erschienen in:
2013 | OriginalPaper | Buchkapitel
11. Semijoins and Antijoins
verfasst von : Karen Morton, Kerry Osborne, Robyn Sands, Riyaj Shamsudeen, Jared Still
Erschienen in: Pro Oracle SQL
Verlag: Apress
Aktivieren Sie unsere intelligente Suche, um passende Fachinhalte oder Patente zu finden.
Wählen Sie Textabschnitte aus um mit Künstlicher Intelligenz passenden Patente zu finden. powered by
Markieren Sie Textabschnitte, um KI-gestützt weitere passende Inhalte zu finden. powered by
Abstract
Semijoins and antijoins are two closely related join methods (options of join methods, actually) that the Oracle optimizer can choose to apply when retrieving information. The SQL language is designed to specify the set of data the user wishes to retrieve, but to leave the decisions regarding how to navigate to the data up to the database itself. Therefore, there is no SQL syntax to invoke a particular join method specifically. Of course, Oracle does provide the ability to give the optimizer directives via hints. In this chapter, I explain these two join optimization options, the SQL syntax that can provoke them, requirements for and restrictions on their use, and, last, some guidance on when and how they should be used.