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    • 1. 发明授权
    • Outerjoin and antijoin reordering using extended eligibility lists
    • 使用扩展资格清单进行外联和反连接重新排序
    • US06665663B2
    • 2003-12-16
    • US09809846
    • 2001-03-15
    • Bruce Gilbert LindsayGuy Maring LohmanMir Hamid PiraheshJun Rao
    • Bruce Gilbert LindsayGuy Maring LohmanMir Hamid PiraheshJun Rao
    • G06F1730
    • G06F17/30466G06F17/30469Y10S707/99934
    • An optimization technique that reorders outerjoins and antijoins with inner joins in a bottom-up optimizer of a relational database management system (RDBMS). Each join predicate is associated with a normal eligibility list (NEL) that includes tables that are referenced in the join predicate and an extended eligibility list (EEL) that includes additional tables that are referenced in conflicting join predicates. An EEL includes all the tables needed by a predicate to preserve the semantics of the original query. During join enumeration, the optimizer determines whether a join predicate's EEL is a subset of all the tables in two subplans to be merged, i.e., whose EEL is covered. If so, the two subplans are combined using the join predicate. Otherwise, the two subplans cannot be joined. Two approaches are used to reordering: without compensation and with compensation. The “without compensation” approach only allows join reorderings that are valid under associative rules. Thus, the optimizer will not combine subplans using a join predicate whose EEL is not covered. The “with compensation” approach allows two subplans to be combined using the join predicate, when a join predicate's EEL is not covered, as long as the join predicate's NEL is covered. Compensation is performed through nullification and best match. Multiple compensations may be merged and performed at any time.
    • 在关系数据库管理系统(RDBMS)的自下而上优化器中,通过内部联接重新排列外部联结和反联合的优化技术。每个连接谓词与正常资格列表(NEL)相关联,包括在连接谓词中引用的表 以及扩展资格列表(EEL),其中包括在冲突的连接谓词中引用的其他表。 EEL包括谓词所需的所有表,以保留原始查询的语义。 在连接枚举期间,优化器确定连接谓词的EEL是否是要合并的两个子计划中的所有表的子集,即其EEL被覆盖。 如果是这样,则使用连接谓词组合两个子计划。 否则,两个子计划不能加入。 两种方法用于重新排序:无补偿和补偿。 “无补偿”方法仅允许在关联规则下有效的连接重排序。 因此,优化器不会使用不包括EEL的连接谓词来组合子计划。 只要连接谓词的NEL被覆盖,“附加补偿”方法允许使用连接谓词组合两个子计划,当连接谓词的EEL不被覆盖时。 赔偿通过无效和最佳匹配执行。 可以随时合并和执行多重补偿。