Abstract: Optimizing query statements in relational databases including determining filtering performance for each of at least two complex predicates in a predetermined layer of the query statement based on a result of a query performed on predetermined data records by using only the complex predicate. The results are ranked based on the filtering performance and re-ordered so that a complex predicate with a higher filtering performance is ranked before a complex predicate with a lower filtering performance. These techniques produce shortened data query response times and improved execution efficiency.

Abstract: Apparatuses and methods for optimizing access path are provided. Execution of a query statement is sampled to obtain the information about a plurality of executing instances, the information about each executing instance comprises the literal value of the query statement in the instance and the filter factor corresponding to the literal value. The plurality of instances are grouped into a plurality of groups based on the filter factors corresponding to the literal values. The average filter factor of each group and the occurrence frequency of the group are obtained. The candidate access path created for the average filter factor of each group is accordingly obtained, and by taking the occurrence frequencies as weights, the weighted execution cost of each candidate access path is calculated for each group. The candidate access path with the minimum sum of the weighted execution costs for all groups is determined as the optimal access path.

Abstract: Optimizing query statements in relational databases including determining filtering performance for each of at least two complex predicates in a predetermined layer of the query statement based on a result of a query performed on predetermined data records by using only the complex predicate. The results are ranked based on the filtering performance and re-ordered so that a complex predicate with a higher filtering performance is ranked before a complex predicate with a lower filtering performance. These techniques produce shortened data query response times and improved execution efficiency.