Consider this:

select 1 as oldid, 2 as id into #tmp;
update #tmp set id=oldid, oldid=0;

Is it guaranteed that id will be non-zero? I.e. is it guaranteed that
the order of assignments in an update matches the order they are
written in?

In article <wwpt5h5o30.fsf (AT) hellcat (DOT) itga.com.au>, gnb (AT) itga (DOT) com.au says...
Probably depends on your database version, but in ASA 7, the assignment
order is NOT guaranteed.

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Gregory Bond <gnb (AT) itga (DOT) com.au> wrote


The order of assignments doesn't matter when it comes to
column values. The values on the RHS are taken from the
original state of the table.

If you did this:

select 1 as oldid, 2 as id into #tmp;
update #tmp set id = oldid, oldid = id
select * from #tmp

you should get id = 1 oldid = 2

The rules are different when variables are involved.
It is best not to rely on placement in that case - instead
write two update statements in the order you want the
updates to occur.

-bret