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Abstract

A database system implementing a methodology or technique that can be used to optimize processing of nested loop joins of three or more tables (n-ary NLJs for n>2) more efficiently is described. In implementation, upon encountering a failure condition (i.e., a given join condition does not hold true) from a join operator (scan child), context information (about the failure) is returned (to the n-ary nested-loop join operator) for indicating exactly which condition (i.e., join condition) failed. This information is tracked in a scan descriptor, which includes a 'fail sarg' data field indicating exactly which particular search argument ('sarg') failed. Based on this information, the system (operating through the n-ary nested-loop join operator) knows exactly which scan child to return back to (i.e., how far back to go in the join order to fetch the next row). In this manner, the methodology optimizes processing of n-ary nested loop joins by eliminating comparisons that will not hold true for the corresponding join condition (for which the comparisons were to be tested).

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First Claim