9. A system for selecting a join order, the system comprising: means for computing a value of a Sigma metric for each of all possible join orders for a query with two or more foreign key--foreign key or foreign key--primary key join operations; and means for selecting a join order having a minimum computed value of the Sigma metric.
9. A system for selecting a join order, the system comprising: means for computing a value of a Sigma metric for each of all possible join orders for a query with two or more foreign key--foreign key or foreign key--primary key join operations; and means for selecting a join order having a minimum computed value of the Sigma metric. 11. The system of claim 9, further comprising: means for selecting a join order from among the possible join orders; means for obtaining an estimate of the cardinality of each component join in the selected join order; and means for calculating a value for Sigma by summing each of the cardinality estimates.