SET NOSTATISTICS tablename tells the query optimizer to ignore any statistics found in IIHISTOGRAMS or IISTATISTICS for the specified table and to use its default values.

SET STATISTICS tells the query optimizer to use any statistics found in IIHISTOGRAMS or IISTATISTICS for the specified table.

The default is for the query optimizer to use statistics.

SET [NO]STATISTICS permanently modifies the table definition and affects queries in future sessions, so its use is restricted to the table owner and DBA.