9. A method for optimizing a database query in a computer of the type including a database management system, the database query involving a plurality of join operations and a plurality of search conditions, the method comprising the steps of, in the computer: applying transitive closure analysis to the plurality of search conditions in the query to determine a subset of equivalent search fields; rewriting a criteria, that operates to re-order a result set of the database query, to generate a set of respective modified criteria that each reference one or more equivalent search fields, wherein the criteria is one of a GROUP BY clause and an ORDER BY clause; identifying a subset of the respective modified criteria that reference a single, respective table; and selecting a join order from among a plurality of join orders for the plurality of join operations, including analyzing join orders using at least one of the set of respective modified criteria.
9. A method for optimizing a database query in a computer of the type including a database management system, the database query involving a plurality of join operations and a plurality of search conditions, the method comprising the steps of, in the computer: applying transitive closure analysis to the plurality of search conditions in the query to determine a subset of equivalent search fields; rewriting a criteria, that operates to re-order a result set of the database query, to generate a set of respective modified criteria that each reference one or more equivalent search fields, wherein the criteria is one of a GROUP BY clause and an ORDER BY clause; identifying a subset of the respective modified criteria that reference a single, respective table; and selecting a join order from among a plurality of join orders for the plurality of join operations, including analyzing join orders using at least one of the set of respective modified criteria. 12. The method according to claim 9 , further comprising the step of: identifying a subset of the respective modified criteria that reference a single, respective table and for which an index is to be created.