| 摘要 |
PURPOSE: To provide a data base join method efficient especially for almost all special instances by a special method which extends and processes an efficient join method. CONSTITUTION: With respect to processing of individual tuples in an outer table (T1 ) 17 which is performed for the purpose of executing outer join of a data base table, all tuples in responsible areas 12 to 15 of an inner table (T2 ) 16 are preserved in the join output, and all tuples in the table T2 which have values smaller than the value of a set of lowest columns in the table T1 in the initial stage are preserved in the join output, and all tuples in the table T1 which are not preserved are preserved up to the last tuple of the table T1 ; and if the table T1 has duplicate values for the value of a set of columns, only last one of duplicate values is preserved in a corresponding tuple of the table T2 .
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