9.2. The ISO Half-Open Interval Model
The display formats for temporal data are defined by the ISO-8601 Standard. The display formats are important, of course, but even more important is the underlying model of durations. They are considered to be half-open intervals. That means that we have an exact point in time when an event starts, but we can only approach the end of it as a limit. To make that clearer, consider the date 2006-12-31 as a shorthand for the interval (2006-12-31 00:00:00 through 2006-12-31 23:59:59.999...). There is no such time as “2006-12-31 24:00:00” in this model; technically, the hour does not exist, and you meant to say “2007:01-01 00:00:00” instead.
DB2 and other SQL products allow a timestamp whose time part is 24:00:00.000000. ...
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