Abstract: There is provided a computer-implemented method of optimizing a query. An exemplary method comprises receiving a first query configured to generate a result set. The query may comprise an operation for an outer table, a first predicate, and a second predicate. The second predicate may comprise a subquery correlated to the operation. Additionally, the first predicate and the second predicate may be disjunctive. The exemplary method also comprises generating a first query tree representing the first query, and generating a second query tree representing a second query. The second query may be configured to generate the result set, and may not comprise the subquery. The exemplary method additionally comprises generating a query plan based on the second query tree.

Abstract: One embodiment relates to a computer-implemented method to estimate a cardinality of a database query. Single table cardinalities are determined after application of selection predicates. In addition, pair-wise join selectivities are estimated without assuming independence between selection and join predicates. Said pair-wise join selectivities are multiplied with said single table cardinalities after application of the selection predicates. Another embodiment relates to a computer apparatus including a cardinality estimator. The cardinality estimator includes computer-readable instructions configured to (a) determine single table cardinalities after application of selection predicates from the database query, (b) estimate pair-wise join selectivities without assuming independence between the selection predicates and join predicates of the database query, and (c) multiply said pair-wise join selectivities with said single table cardinalities after application of the selection predicates.

Abstract: There is provided a computer-implemented method of optimizing a query. An exemplary method comprises receiving a first query configured to generate a result set. The query may comprise an operation for an outer table, a first predicate, and a second predicate. The second predicate may comprise a subquery correlated to the operation. Additionally, the first predicate and the second predicate may be disjunctive. The exemplary method also comprises generating a first query tree representing the first query, and generating a second query tree representing a second query. The second query may be configured to generate the result set, and may not comprise the subquery. The exemplary method additionally comprises generating a query plan based on the second query tree.

Abstract: A database query is submitted to a first query optimizer to receive a first query plan from the first query optimizer. The first query plan is set as a current query plan. As an entry point, the current query plan is executed against the database within a given environment of the database. Where execution of the current query plan within the given environment is problematic, the execution of the current query plan is prematurely terminated, and the database query is submitted to a second query optimizer. Where a second query plan that is different than any previous query plan for the database query has been received from the second query optimizer, the second query plan is set as the current query plan, and a risk to the database in executing the current query plan is determined. Where the risk is less than a threshold, the entry point is proceeded to.

Abstract: There is provided a system and method for performing testing on a database system comprising a query optimizer, the query optimizer having an optimizer plan space comprising a plurality of query plans. An exemplary method comprises generating a plurality of queries programmatically according to a template query by varying at least one of an operation, a predicate or a parameter to produce a plurality of query plans. The exemplary method also comprises optimizing the plurality of queries using the query optimizer to collect the plurality of query plans and selecting a subset of queries from the plurality of queries using the query optimizer, the subset of queries comprising queries with distinct query plans that substantially cover the optimizer plan space. The exemplary method additionally comprises executing the subset of queries on the database system to identify an inefficiency of the database system.

Abstract: One embodiment relates to a computer-implemented method to estimate a cardinality of a database query. Single table cardinalities are determined after application of selection predicates. In addition, pair-wise join selectivities are estimated without assuming independence between selection and join predicates. Said pair-wise join selectivities are multiplied with said single table cardinalities after application of the selection predicates. Another embodiment relates to a computer apparatus including a cardinality estimator. The cardinality estimator includes computer-readable instructions configured to (a) determine single table cardinalities after application of selection predicates from the database query, (b) estimate pair-wise join selectivities without assuming independence between the selection predicates and join predicates of the database query, and (c) multiply said pair-wise join selectivities with said single table cardinalities after application of the selection predicates.