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IMO the problem is the database design. Historical ownership can not
be correctly represented with only a transaction time. Such historical
ownership would be a duration. The ownership table also fails to denote
that the *STORE is the owner between transactions which would complete
known ownership history.
I would define the OWNER table to have a column for both a FROM_TMSP
and UNTIL_TMSP to designate the duration that the item is owned; the end
of the duration is CURRENT TIMESTAMP when not defined. Having done so,
the problem of designating the OWNER for each sequential [historical]
timestamped event should be more easily grasped, as ordered results of a
LEFT OUTER JOIN WHERE EVENT_TMSP BETWEEN FROM_TMSP AND UNTIL_TMSP The
range for selection is defined in a row, rather than between that and a
prior row.
SELECT i.*, o.owner
FROM INVENTORY I
LEFT OUTER JOIN OWNER O
WHERE i.tmsp BETWEEN o.from_tmsp
AND ifnull(o.until_tmsp, current timestamp)
AND o.owner <> '*STORE'
An insert trigger on the OWNER file can enforce the rule that both
the previous historical until-time and the new historical from-time will
get the same timestamp value, and that the until-time of the new row
gets the NULL value since the until-time for the current owner is
indeterminate until the next insert defining the start of the next
duration of ownership.
Regards, Chuck
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This thread ...
RE: Need ideas for SQL join select to replace logical view, (continued)
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