In this example, the time zone displacement specified in the literal, INTERVAL '04:00' HOUR TO MINUTE, is used to determine the UTC value '04:30:00' for the TIME literal.
The result of the CAST is the time formed from the time portion of the source expression value '04:30:00' at UTC, and the specified time zone displacement, INTERVAL -'08:00' HOUR TO MINUTE.
The result value of the CAST '04:30:00' at UTC is adjusted to its time zone displacement, INTERVAL -'08:00' HOUR TO MINUTE, and the result of the SELECT statement is: TIME '20:30:00-08:00'.
This result of the SELECT statement is equal to TIME '04:30:00+00:00'. The current session time zone displacement, INTERVAL '08:00' HOUR TO MINUTE, has no effect.
SET TIME ZONE INTERVAL '08:00' HOUR TO MINUTE; SELECT CAST(TIME '08:30:00+04:00' AS TIME(0) WITH TIME ZONE AT -8);