1. A method for generating a query plan for estimating a number of unique entry counts of an attribute in a database, said method comprising: identifying a sample of entries in the database; calculating a skewness of the entries in the sample; identifying, by a processor, a sampling percent of the sample; selecting at least one of a plurality of estimators based upon the calculated skewness of the entries and based upon whether the sampling percent of the sample is equal to or exceeds a predetermined percentage value; and generating a query plan from the selected at least one of the plurality of estimators, wherein the query plan is to be implemented in estimating the number of unique entry counts of the attribute.