Efficient optimization of a class of relational expressions

Authors:
A. V. Aho;Y. Sagiv;J. D. Ullman
Affiliations:
Bell Laboratories, Murray Hill, New Jersey;Princeton University, Princeton, New Jersey;Princeton University, Princeton, New Jersey
Venue:
SIGMOD '78 Proceedings of the 1978 ACM SIGMOD international conference on management of data
Year:
1978

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Abstract

Many useful database queries can be formulated in terms of expressions whose operands are relations and whose operators are the relational operations select, project, and join. This paper investigates the computational complexity of optimizing relational expressions of this form under a variety of cost measures. A matrix, called a tableau, is proposed as a conventient representative for the value of an expression. Functional dependencies can be used to imply additional equivalences among tableaux. The optimization problem is shown to be NP-complete, but we can give a polynomial time algorithm to optimize tableaux that correspond to an important subclass of expressions.