QUERY OPTIMIZER WITH JOIN CARDINALITY ESTIMATION WHICH MITIGATES THE EFFECTS OF SKEW

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. Other embodiments, aspects and features are also disclosed.