| 摘要 |
An optimizer-code generator for use in a data base system. The optimizer-code generator employs a component called a scan analyzer for performing implementation-dependent analysis and providing implementation-dependent query code. The optimizer-code generator receives a query in logical tree form. It first optimizes the logical tree. In so doing, it provides information from the logical tree to the scan analyzer, which specifies what methods are available for accessing information required for the query and what each of the available methods costs. The optimizer-code generator uses the cost information in its optimization of the logical tree and specifies the access methods to be used in the logical tree. The code generator then uses the logical tree to generate query code. In so doing, it provides the specifications of the access methods to the scan analyzer, which returns query code for the access method. The code generator then incorporates the query code for the access method in the query code which it generates from the logical tree.
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