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ICDE
2007
IEEE

Unnesting Scalar SQL Queries in the Presence of Disjunction

11 years 1 months ago
Unnesting Scalar SQL Queries in the Presence of Disjunction
Optimizing nested queries is an intricate problem. It becomes even harder if in a nested query the linking predicate or the correlation predicate occurs disjunctively. We present the first unnesting strategy that can effectively deal with such queries. The starting point of our approach is to translate SQL into the relational algebra extended by bypass operators. Then we present for the first time unnesting equivalences which are valid for algebraic expressions containing bypass operators. Applying these to the translated queries results in our effective unnesting strategy for nested SQL queries with disjunction. With an extensive experimental study (including three commercial DBMSs), we demonstrate the possible performance gains of our approach.
Matthias Brantner, Norman May, Guido Moerkotte
Added 01 Nov 2009
Updated 01 Nov 2009
Type Conference
Year 2007
Where ICDE
Authors Matthias Brantner, Norman May, Guido Moerkotte
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