Abstract
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.
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© 1994 Springer-Verlag Berlin Heidelberg
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Steenhagen, H.J., Apers, P.M.G., Blanken, H.M. (1994). Optimization of nested queries in a complex object model. In: Jarke, M., Bubenko, J., Jeffery, K. (eds) Advances in Database Technology — EDBT '94. EDBT 1994. Lecture Notes in Computer Science, vol 779. Springer, Berlin, Heidelberg. https://doi.org/10.1007/3-540-57818-8_62
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DOI: https://doi.org/10.1007/3-540-57818-8_62
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