| 摘要 |
Data in materialized query tables (MQTs) are used as statistics for determining the optimal execution plan for a query. When an MQT is defined, it is examined to determine whether its data provides statistics for determining an optimal execution plan for a query. If so, then the MQT is identified, in the RDBMS, as a source for statistics. Information needed to exploit the MQT data as statistics is cataloged in the RDBMS. This information includes a characterization of the type of statistics provided by the MQT, the table and column distributions represented by those statistics, and a query for later retrieving relevant data from the MQT during the query optimization process. When a query is accepted for execution, the cataloged relevant information about MQTs is examined to determine whether an MQT exists that provides statistics relevant to optimization of the query. If such an MQT exists, then the relevant data is retrieved from the MQT using the cataloged query. Using the retrieved statistics, an optimal execution plan may be determined for the query.
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