Optimization of nested queries in a complex object model
| Autor: | Steenhagen, Hennie J., Apers, Peter M.G., Blanken, Henk, Jarke, Matthias, Bubenko, Janis, Jeffery, Keith |
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| Jazyk: | angličtina |
| Rok vydání: | 1994 |
| Předmět: | |
| Zdroj: | Advances in database technology-EDBT '94, 337-350 STARTPAGE=337;ENDPAGE=350;TITLE=Advances in database technology-EDBT '94 Advances in Database Technology — EDBT '94 ISBN: 9783540578185 EDBT |
| Popis: | Transformation of nested SQL queries into join queries is advantageous because a nested SQL query can be looked upon as a nested-loop join, which is just one of the several join implementations that may be available in a relational DBMS. In join queries, dangling (unmatched) operand tuples are lost, which causes a problem in transforming nested queries having the aggregate function COUNT between query blocks-a problem that has become well-known as the COUNT bug. In the relational context, the outerjoin has been employed to solve the COUNT bug. In complex object models supporting an SQL-like query language, transformation of nested queries into join queries is an important optimization issue as well. The COUNT bug turns out to be a special case of a general problem being revealed in a complex object model. To solve the more general problem, we introduce the nest join operator, which is a generalization of the outerjoin for complex objects. |
| Databáze: | OpenAIRE |
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