|Subject||Re: [Firebird-Architect] the insert into t select * from t infinite|
> Hi,Are 5 or 10 records
> > Here's a particularly nasty query (at least I think it is)
> > delete from t t1
> > where t1.id in (select first 5 t t2
> > from t order by t2.id);
> > If we applied the logic I described above (assuming it can be applied)
> > here's what happens. Still assuming an index on t.id, the engine starts
> > reading the index and finds that the first five entries are all valid,
> > and that the first one matches the value of t.id from the outer loop so
> > that record is deleted. It gets the next value of t.id and goes to the
> > index to find the first 5 records. The first record appears, at first
> > glance, to be deleted, but it is also on the undo list for the delete.
> > The engine goes to the previous version of that record, finds that it is
> > legitimate for the current transaction, and keeps it in the list of 5.
> > Again, the non-indexed case has the same behavior at greater cost.
> What is the list of 5?
> What happends when the statement is executed twice in the same transaction?
> deleted?Each statement executed under it's own savepoint (verb).
So - each execution will delete 5 records (if present)