When you enable and collect workload statistics, the system
    table, RDB$WORKLOAD, is created and populated. (See Collect_
    Optimizer_Statistics for details.) If you are knowledgeable
    about the data in your database, or if workload statistics were
    gathered for queries that are no longer in use, you might decide
    that you no longer want Oracle RMU to collect statistics for
    particular column groups. The RMU Delete Optimizer_Statistics
    gives you the ability to selectively delete records for column
    groups in the RDB$WORKLOAD system table.

    When you use the RMU Delete Optimizer_Statistics command, both
    the optimizer statistics themselves and the reference to the
    column duplicity factor and the null factor are deleted from the
    RDB$WORKLOAD system table.

    If you issue an RMU Collect Optimizer_Statistics command after
    having issued an RMU Delete Optimizer_Statistics command,
    statistics for the specified column group are not collected.