Abstract: A method, apparatus, and computer program product for executing a relational database management system (RDBMS) in a computer system, wherein the RDBMS manages a relational database comprised of one or more tables storing data. The RDBMS executes a query with a semi-join operation comprising an inclusion join and/or an exclusion join performed against at least an outer table and an inner table, wherein the inclusion join returns a row from the outer table when there is a match with a row in the inner table, and the exclusion join returns a row from the outer table when there is no match with a row in the inner table. The RDBMS performs a rewrite of the query to avoid spooling and/or sorting of the inner table, when the inner table is larger than the outer table and a cost after the rewrite is lower than before the rewrite.

Abstract: A method for determining the cost of evaluating queries against a database. The method includes receiving a condition, or query; determining the cost of one or more fixed cost operators within the condition; and determining the cost of one or more variable coefficients within the condition. The method may also be extended to determine the cost of successive conditions within a set of conditions as a function of the cost of a current condition and the combined selectivity of previous conditions within the set of conditions; and to determine an optimal order of conditions within a set of conditions.