When generating statistics for a database, by default all rows of the selected tables are used in the generation of statistics. These non-sampled statistics represent the most accurate statistics possible, because all data is considered.

When the base table is large, you may want to use sampled statistics. With a sufficient sampling, statistics created are almost identical to statistics created on the full table. The processing for sampled statistics is discussed in greater detail in Sampled Optimizer Statistics.

In VDBA, to specify a percentage of rows to be sampled, enable Statistics on Sample Data check box, and specify the percentage using the Percentage control in the Optimize Database dialog.