Artificial Intelligence
The equivalence of solving queries and producing tree projections (extended abstract)
PODS '86 Proceedings of the fifth ACM SIGACT-SIGMOD symposium on Principles of database systems
Principles of database and knowledge-base systems, Vol. I
Principles of database and knowledge-base systems, Vol. I
Optimization of large join queries
SIGMOD '88 Proceedings of the 1988 ACM SIGMOD international conference on Management of data
Optimization of large join queries: combining heuristics and combinatorial techniques
SIGMOD '89 Proceedings of the 1989 ACM SIGMOD international conference on Management of data
On the optimality of strategies for multiple joins
PODS '90 Proceedings of the ninth ACM SIGACT-SIGMOD-SIGART symposium on Principles of database systems
Decomposition—a strategy for query processing
ACM Transactions on Database Systems (TODS)
On the Desirability of Acyclic Database Schemes
Journal of the ACM (JACM)
Access path selection in a relational database management system
SIGMOD '79 Proceedings of the 1979 ACM SIGMOD international conference on Management of data
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Avoiding Cartesian products is a common heuristic to reduce the search space of join expressions (orderings) over some set of relations. However, this heuristic cannot guarantee optimal join expressions in its search space because the cheapest Cartesian-product-free (CPF, for short) join expression could be significantly worse than an optimal non-CPF join expression. In a recent PODS, Tay [9] gave some conditions on actual relations that ensure the existence of an optimal CPF join expression; however, the conditions turn out to be applicable only in special cases. In this paper, we do not put any restrictions on actual relations, and we introduce a novel technique that derives programs consisting of joins, semijoins, and projections from CPF join expressions. Our main result is that for every join expression, there exists an equivalent CPF join expression from which we can derive a program whose cost is within a constant factor of the cost of an optimal join expression.