--- In firebird-support@yahoogroups.com, "dinol.softedge" <dinol@...>
wrote:

>
> Hi Nick
>
> Thanks for your response. Why do you say the statement is a recipe for
> disaster in a multiuser environment?

Because your triggers presume that two or more people can not buy the
same inventory item at the same time (this may be true, we don't know
your environment).

To avoid dirty writes, only a single transaction would be able to
update a single record in TBL_LOC_INV at a time, and no other
transaction can perform an update on the same table until after the
first transaction commits, and no contemporary transaction with an
older view of that record could update it ever.

Now if you update these batch movements at the end of all your user
activities, then they may occur fast enough to make serialisation with
retry logic feasible, however if you write this in such a way that you
update TBL_MOVEMENT_BU from the one transaction over more than a few
seconds (eg, as each item is scanned at a register), you are in for
some tears.

Adam