If you use either the FROM ERROR TABLE FOR data_table_name syntax or the example for the FROM error_table_name syntax, then the information returned is for the column you specify in the error table associated with data_table_name, not from the base table specified by data_table_name.
The HELP COLUMN information and attributes reported by either of these syntaxes is identical to that returned by the other HELP COLUMN syntaxes, only for an error table rather than for a base data table.
See CREATE ERROR TABLE for more information about error tables.
Also see HELP ERROR TABLE.