Dennis Bjorklund <db@zigo.dhs.org> writes:
> The standard treat days as a separate entry, it does not assume that a day
> is 24 hours.
SQL92 says
4.5.2 Intervals
There are two classes of intervals. One class, called year-month intervals, has an express or implied
datetimeprecision that in- cludes no fields other than YEAR and MONTH, though not both are required. The
otherclass, called day-time intervals, has an ex- press or implied interval precision that can include any
fields other than YEAR or MONTH.
AFAICS the reason for this rule is that they expect all Y/M intervals to
be comparable (which they are) and they also expect all D/H/M/S intervals
to be comparable, which you can only do by assuming that 1 D == 24 H.
It seems to me though that we can store days separately and do interval
comparisons with the assumption 1 D == 24 H, and be perfectly
SQL-compatible as far as that goes, and still make good use of the
separate day info when adding to a timestamptz that has a DST-aware
timezone. In a non-DST-aware timezone the addition will act the same as
if we weren't distinguishing days from h/m/s. Therefore, an application
using only the spec-defined features (ie, only fixed-numeric-offset
timezones) will see no deviation from the spec behavior.
regards, tom lane