SKEW SENSITIVE ESTIMATING OF RECORD CARDINALITY OF A JOIN PREDICATE FOR RDBMS QUERY OPTIMIZER ACCESS PATH SELECTION

A query optimizer receives a relational database management system (RDBMS) query having a join predicate with a join between a first and a second table. The query optimizer determines a high skew value for a first variable joining the first and second tables at columns per the join predicate. A count query on one of the first and second tables is constructed and run only using the high skew value as a substitution for the first variable. A quantity of records for the join of the first and second tables is estimated using results of the count query. Different access paths (e.g., query plans) are used by the query optimizer depending on whether the estimated quantity of records exceeds a previously determined threshold or not.