Importance

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Abstract

A computer database system utilizes a method for performing a right outer join of database tables without sorting the inner table (T.sub.2). The processing of each tuple in the outer table (T.sub.1) includes the preservation in the joint output of all tuples in T.sub.2 which are in its responsibility region. The initialization step of the process preserves in the join output all of the tuples in T.sub.2 which have column set values less than the lowest column set value in T.sub.1, i.e. the first tuple in T.sub.1, since T.sub.1 is sorted or accessed using a sorted index. The responsibility region for tuples in T.sub.1, other than the last tuple, is defined as those tuples which have column set values less than the column set value for the next tuple in T.sub.1 and greater than or equal to the column set value for the current T.sub.1 tuple. The last tuple in T.sub.1 must preserve all of the tuples in T.sub.2 which have not already been preserved in T.sub.2, i.e. all tuples greater than or equal to its column set value. If T.sub.1 has duplicate values for the column set value, only the last one preserves the associated T.sub.2 tuples. Additional methods for parallel execution of the outer join methods and methods for applying the outer join methods to subqueries (i.e., an All (or universal) Right Join (ARJOIN) and an Existential Right Join (ERJOIN)) are described.

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