A DATE value can be cast as PERIOD(DATE) or PERIOD(TIMESTAMP[(n)] [WITH TIME ZONE]) using the CAST function. If an attempt is made to cast a DATE value as PERIOD(TIME[(n)] [WITH TIME ZONE]), an error is reported.
If the target type is PERIOD(DATE), the result beginning element is set to the source value. The result ending element is set to the result beginning bound plus one granule of the target type (that is, INTERVAL '1' DAY). If the result ending bound exceeds the maximum DATE value (that is, the source value is equal to the maximum DATE value), or the result ending bound equal to maximum DATE value (that is, the resulting ending bound value equal to value of UNTIL_CHANGED) an error is reported.
If the target type is PERIOD(TIMESTAMP[(n)]), the result beginning element is set to the UTC value obtained using the current session time zone and a timestamp value formed from the source DATE value and a time portion of zero. The result ending element is set to the result beginning bound plus one granule of the target type (note that this cannot cause an error).
If the target type is PERIOD(TIMESTAMP[(n)] WITH TIME ZONE), the time portion of the result beginning element is set to the UTC value obtained using the current session time zone and a timestamp value formed from the source DATE value and a time portion of zero. The time zone of the result beginning element is set to the current session time zone displacement. The result ending element is set to the result beginning bound plus one granule of the target type (note that this cannot cause an error).