| 摘要 |
PURPOSE: To efficiently and effectively execute optimization based on an inquiry cost to a relation inquiry in the case an external function is present by utilizing cost information and accessing a relational data base and the external function provided with a declaration type rewrite rule. CONSTITUTION: A relational data base system 2 receives an inquiry 10 to be optimized and the inquiry 10 is supplied to an optimizer 11 for optimizing the inquiry 10 corresponding to a rewrite rule 12 and the cost information 13. The optimizer 11 receives the inquiry 10 to be processed, generates an alternate inquiry by using the rewrite rule 12 and further, selects an optimum plan from an inquiry group including the received inquiry and the alternate inquiry. In the relational data base system 2, a relational execution engine 14 capable of accessing a relational data base table 15 and the external function 16 is provided as well and the rewrite rule 12 is related to the external function 16.
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