RE: Need ideas for SQL join select to replace logical view

["Joe Pluta" <joepluta@xxxxxxxxxxxxxxxxx>]

> From: CRPence
>
>    IMO the problem is the database design.  Historical ownership can not
> be correctly represented with only a transaction time.

And yet, with a simple ISAM access, we can generate the required report with
the existing database.  It seems to me that it is NOT the database design
that is at fault, but simply the wrong choice of tool.


> 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.

That's all well and good, but it also requires more fields as well as extra
writes to the database.  It's hard to consider a database design better than
another if it increases both storage requirements and workload.

I'm not saying your solution doesn't work, just that it is not without its
own problems.  And sometimes changing the database just isn't an option.
That's when ISAM really shines - when your data isn't perfect.



>    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.

Also, there is an inherent problem here.  BETWEEN is inclusive, so that if
the from timestamp of one period matches the until timestamp of the previous
period (as you suggest), then events with that same timestamp will be
included in both ranges.

You can get around this with date >= from and < until.

Joe