Abstract: A database management system predicts a selectivity for database query conditions requiring a join of records from different tables. The system identifies at least one skewed value in a field specified in the join condition, and constructs, for each skewed value, a set of hypothetical query predicates in which the field specified in the join condition is replaced with a constant equal to the skewed value. The system then predicts the selectivity for the hypothetical predicates, using any appropriate prediction technique. The selectivities of the hypothetical predicates are used to predict a selectivity for the original query.

Abstract: A database management system predicts a selectivity for database query conditions requiring a join of records from different tables. The system identifies at least one skewed value in a field specified in the join condition, and constructs, for each skewed value, a set of hypothetical query predicates in which the field specified in the join condition is replaced with a constant equal to the skewed value. The system then predicts the selectivity for the hypothetical predicates, using any appropriate prediction technique. The selectivities of the hypothetical predicates are used to predict a selectivity for the original query.

Abstract: The present invention is a low power and low heat dissipating, low illumination system that is based in an electrical box cover plate, preferably in a light switch cover plate. It allows for the maintenance of an electrical bleed current through the fluorescent light controlled by that light switch so as to keep a minimal thermal differential between the unlit and lit light. The light switch cover plate has a series of imbedded LEDs that illuminate an area all around the light switch. The unit is retrofittable on conventional light switches.

Abstract: Disclosed is a night lighting system retrofittable with existing wall switches for illuminating an area around the wall switches. The night lighting system comprises: a wall plate having at least one switch receiving slot capable of receiving a switch, at least one lens assembly disposed on the wall plate, a printed circuit board having at least one light emitting diode and interface wires electrically connecting the night lighting system to a power switch. The lens assembly has a chamber protruding from a back surface of the wall plate, and a lens covering a front end of the chamber. The chamber is capable of receiving at least a portion of the light emitting diode, such that, light from the light emitting diode passes-though the lens to illuminate an area around the switch.

Abstract: An apparatus, program product and method generate at least one statistic for a temporary table during optimization of a database query before the temporary table is created. By doing so, optimization can proceed on a database query irrespective of the fact that the temporary table may not be materialized until the database query is ultimately executed.

Abstract: Building database statistics for use by a query optimizer is beneficial but may over utilize system resources. Accordingly, the frequency that statistics are rebuilt is controlled in order to minimize the effect of the system. In particular, the staleness of the data and the time since the last statistics collection are used to determine whether or not to re-collect statistics. Even for relatively stale data, statistics are not rebuilt until a predetermined time period has passed.

Abstract: A database management system predicts a selectivity for database query conditions requiring a join of records from different tables. The system identifies at least one skewed value in a field specified in the join condition, and constructs, for each skewed value, a set of hypothetical query predicates in which the field specified in the join condition is replaced with a constant equal to the skewed value. The system then predicts the selectivity for the hypothetical predicates, using any appropriate prediction technique. The selectivities of the hypothetical predicates are used to predict a selectivity for the original query.

Abstract: Mirroring database statistics, including receiving by a backup application of a backup computer a journal entry representing a requirement for backup database statistics and generating by a statistics engine of the backup computer backup database statistics for a backup database in accordance with the journal entry. Mirroring database statistics according to embodiments of the present invention may also include identifying by an original DBMS of an original database a requirement for backup database statistics and inserting in a database journal by the original DBMS the journal entry representing the requirement for backup database statistics.

Abstract: A database management system associates, for one or more database fields, a respective representation of cardinality with different discrete subsets of database records, the subsets preferably being defined by different quantiles of an equal height histogram. The system predicts a relative number of records responsive to a query condition using the representation of cardinality of a quantile in which a query-specified value lies. Preferably, a relative number of responsive records is estimated as a quantile size representation divided by a cardinality representation. The system uses this prediction to determine an optimum query execution strategy. Preferably, the system derives histogram data including cardinality and ordinal numbers corresponding to each quantile using sampling techniques.

Abstract: A database query optimizer determines when no optimal index for a query exists, determines whether a sub-optimal index exists, and if so, uses statistical information for each additional key in the sub-optimal index to rewrite the query in a manner that allows traversing the sub-optimal index. The sub-optimal index is then probed using the rewritten query, and the number of estimated returned rows is then used to optimize the query.

Abstract: A cardinality estimator computes an estimated cardinality for a database column using a formula that accounts for skew in the data in the column. The result is an estimate of cardinality that more closely resembles the actual cardinality in the column. The improved cardinality estimate may then be used to make better query optimizations.