Douglas said:
the [DATETIME] data type is not
intended to handle durations: it's meant for timestamps (i.e. specific
points in time). This is because of how [DATETIME] values are stored
No, it has nothing to do with the way the SQL implementation persists
the values e.g. Access/Jet could store DATETIME values as text (as does
one SQL product I have used) and it would make no difference. You got
it right in your first (quoted) sentence i.e. Access/Jet's DATETIME is
synonymous with the TIMESTAMP data type in standard SQL.
Standard SQL has an INTERVAL data type but it has not implemented in
Access/Jet, nor any other SQL product AFAIK. Instead, intervals are
modelled in SQL using pairs of DATETIME (TIMESTAMP) values to model
start and end respectively. Google for the work of Snodgrass on
temporal data in SQL.
Jamie.