If no statistics are available for a column, a message indicates the default selectivity that will be used. This message is printed for an open-ended range query on the total_sales table:
No statistics available for total_sales, using the default range selectivity to estimate selectivity.
Estimated selectivity for total_sales, selectivity = 0.330000.
See “Default values for search arguments” for the default values used for search arguments and “When statistics are not available for joins” for the default values used for joins.
You may be able to improve optimization for queries where default values are used frequently, by creating statistics on the columns.
See “Creating and updating column statistics”.