1. A computer program product comprising a machine-readable medium storing instructions that, when executed by at least one programmable processor, cause the at least one programmable processor to perform operations comprising: applying an estimation algorithm to generate a uniqueness metric representative of data in a column of a database table, the column being split across a plurality of data partitions; classifying the column as categorical or non-categorical by comparing the uniqueness metric to a threshold; assigning one of a first estimation factor and a second estimation factor to the column, the assigning comprising the first estimation factor if the column is classified as categorical and the second estimation factor if the column is classified as non-categorical, the second estimation factor being larger than the first estimation factor; calculating a cost estimate for system resources required to perform a database operation on the database table, the cost estimate comprising an estimated total number of distinct values in the column across all of the plurality of data partitions determined using the assigned first estimation factor or second estimation factor and a number of rows in the table as inputs to an estimation function; and promoting the cost estimate.