PostgreSQL 'TIMESTAMP', for nonextreme values, is the same idea as java.time.Instant -- an absolute point on the timeline stored internally as a number from som

PostgreSQL 'TIMESTAMP', for nonextreme values, is the same idea as java.time.Instant -- an absolute point on the timeline stored internally as a number from some epoch -- but whose default textual interface accepts and emits java.time.LocalDateTime values that correspond, but aren't tagged with the UTC zone. When you insert into a 'TIMESTAMP', it's as if it did input LocalDateTime(x).atZone(UTC).toInstant(), and saved that; and when you read it, it's as if it does storedInstant.atZone(UTC).toLocalDateTime(). A 'TIMESTAMPTZ' is stored the same way, but on string output is converted to the session timezone, and an underspecified input is enriched with the session timezone. When you insert into a 'TIMESTAMPTZ' it'd take the input OffsetDateTime or ZonedDateTime, or enrich the input with the session zone until one were obtained, call .toInstant(), and save it. On read, it'd do storedInstant.atZone(sessionZone) to obtain a ZonedDateTime, and its default output format only includes the offset. LocalDateTime is useful for calendaring, and as an intermediate step when joining a LocalDate and a LocalTime and working towards a Zoned or Instant.