The database system automatically saves basic statistical information on the size of tables and indexes in the internal file directory. On request, the database system also determines a range of additional statistical information, which it saves in the database catalog (this operation is called "updating the statistics"). SQL optimizer uses these statistics to determine the optimum strategy for accessing data in the database when processing complicated SQL statements, such as joins.
Database Administration, SQL Optimizer Statistics
Database Studio, Updating SQL Optimizer Statistics
Database Administration in CCMS, Scheduling the Update of the SQL Optimizer Statistics