Unnesting Arbitrary Queries

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Unnesting Arbitrary Queries
: SQL-99 allows for nested subqueries at nearly all places within a query. From a user’s point of view, nested queries can greatly simplify the formulation of complex queries. However, nested queries that are correlated with the outer queries frequently lead to dependent joins with nested loops evaluations and thus poor performance. Existing systems therefore use a number of heuristics to unnest these queries, i.e., de-correlate them. These unnesting techniques can greatly speed up query processing, but are usually limited to certain classes of queries. To the best of our knowledge no existing system can de-correlate queries in the general case. We present a generic approach for unnesting arbitrary queries. As a result, the de-correlated queries allow for much simpler and much more efficient query evaluation.
Thomas Neumann 0001, Alfons Kemper
Added 17 Apr 2016
Updated 17 Apr 2016
Type Journal
Year 2015
Where BTW
Authors Thomas Neumann 0001, Alfons Kemper
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