ANSI date and time values can be compared only to values of the same type. When the time zone setting of a time or timestamp value does not match that of its comparand, time or timestamp values WITH TIME ZONE or WITH LOCAL TIME ZONE are considered to be stored in GMT and can be compared directly. If one comparand is time or timestamp WITH TIME ZONE or WITH LOCAL TIME ZONE and the other comparand is WITHOUT TIME ZONE, the value of the WITHOUT TIME ZONE comparand is assumed to be in local time of the session default time zone. It is converted to GMT based on that assumption and the comparison proceeds.