UNTIL_CHANGED and UNTIL_CLOSED
UNTIL_CHANGED and UNTIL_CLOSED are special values that represent the ending bound of periods for which the duration is indefinite, forever, or for which the end is an unspecified and unknown time in the future when the row will be changed. They are used in some circumstances when a new row is inserted into a temporal table:
UNTIL_CLOSED has a data type of TIMESTAMP(6) WITH TIME ZONE and a value of TIMESTAMP '9999-12-31 23:59:59.999999+00:00'.
The value of UNTIL_CHANGED depends on the data type and precision of the valid-time column. If the type is PERIOD(DATE), UNTIL_CHANGED is the value DATE '9999-12-31'. If the type is PERIOD(TIMESTAMP), UNTIL_CHANGED is the value of TIMESTAMP '9999-12-31 23:59:59.999999+00:00', with precision and time zone matching that specified for the valid-time data type.
For more information on UNTIL_CHANGED and UNTIL_CLOSED, see the discussion of Period data types in SQL Data Types and Literals.