| 摘要 |
<p>A variety of query optimization techniques are described herein. A first query optimization technique, referred to herein as non-empty transformation, may be applied to queries that specify one or more measures, a dimensional context within which the measure(s) are to be evaluated, and a filter condition specifying that rows with only empty measure values be excluded from a result set. The non-empty transformation technique enables such queries to be rewritten into another format that can be executed more efficiently than the original queries. A second query optimization technique described herein involves restructuring an operator tree representation of a query so as to avoid unnecessary duplicated evaluation of extension columns. A third query optimization technique described herein automatically selects a minimum number of join columns having the lowest cardinality for implementing a join between two tables.</p> |
