Column_Group=(column-list)

    Specifies a list of columns that comprise a single column group.
    The columns specified must be a valid column group for a table
    specified with the Tables=(table-list) qualifier. (Use the RMU
    Show Optimizer_Statistics command to display a valid column
    groups.) When you specify the Column_Group qualifier, the entire
    record in the RDB$WORKLOAD system table that holds data for the
    specified column group is deleted. Therefore, the next time you
    issue the RMU Collect Optimizer_Statistics command, statistics
    for the specified column-group are not collected.