AQuery: query language for ordered data, optimization techniques, and experiments

  • Authors:

  • Alberto Lerner;Dennis Shasha

  • Affiliations:

  • Ecole Nationale Superieure, de Telecommunications, Paris, France;New York University, New York

  • Venue:
  • VLDB '03 Proceedings of the 29th international conference on Very large data bases - Volume 29
  • Year:
  • 2003

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Abstract

An order-dependent query is one whose result (interpreted as a multiset) changes if the order of the input records is changed. In a stock-quotes database, for instance, retrieving all quotes concerning a given stock for a given day does not depend on order, because the collection of quotes does not depend on order. By contrast, finding a stock's five-price moving-average in a trades table gives a result that depends on the order of the table. Query languages based on the relational data model can handle order-dependent queries only through add-ons. SQL:1999, for instance, has a new "window" mechanism which can sort data in limited parts of a query. Add-ons make order-dependent queries di_cult to write and to optimize. In this paper we show that order can be a natural property of the underlying data model and algebra. We introduce a new query language and algebra, called AQuery, that supports order from-the-ground-up. New order-related query transformations arise in this setting. We show by experiment that this framework - language plus optimization techniques - brings orders-of-magnitude improvement over SQL:1999 systems on many natural order-dependent queries.