Unique Value Calculation in Partitioned Table

A system comprising:

• at least one programmable processor;
• and
• a machine-readable medium storing instructions that, when executed by the at least one processor, cause the at least one programmable processor to perform operations comprising:
• assigning a first estimation factor to a column of a database table when a uniqueness metric representative of data in the column is above a threshold value and assigning a second estimation factor to the column when the uniqueness metric representative of the data in the column is not above the threshold value, the second estimation factor being larger than the first estimation factor, the column being split across a plurality of data partitions of the database table;
• 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.

A computer-implemented method comprising:

• assigning a first estimation factor to a column of a database table when a uniqueness metric representative of data in the column is above a threshold value and assigning a second estimation factor to the column when the uniqueness metric representative of the data in the column is not above the threshold value, the second estimation factor being larger than the first estimation factor, the column being split across a plurality of data partitions of the database table;
• 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.