Unique value estimation in partitioned tables

An estimation algorithm can generate a uniqueness metric representative of data in a database table column that is split across a plurality of data partitions. The column can be classified as categorical if the uniqueness metric is below a threshold and as non-categorical if the uniqueness metric is above the threshold. A first estimation factor can be assigned to the column if the column is classified as categorical or a larger second estimation factor can be assigned if the column is non-categorical. A cost estimate for system resources required to perform a database operation on the database table can be calculated. The cost estimate can include 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.