| 摘要 |
PURPOSE:To decrease a large table in an early stage by applying semi-join from a site in relation with the less number of keys into larger site and selecting the minimum reduction rate among plural semi-join candidates. CONSTITUTION:The relation of other site uses a scattered access processing section 8 to recognize the number of taps, field information, index information and key number of join field from a data dictionary of each site, a pre- processing section 4 forms graphic information representing join relation between sites, an optimizing processing section 9 uses a key number estimation section 10 to estimate the key number of join field, a join selection section 11 selects the join having the maximum difference of two key numbers by using the ratio of corresponding two estimated key numbers as to the join related to the side with smaller key number of the two estimated key numbers relating to the join as an index, a command generating section 12 transfers join field information from the site having a smaller key number to the side with the larger key number to apply semi-join processing.
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