Re: Table alias fun == incorrectly adding tables to join...

On Mon, 22 Sep 2003, Sean Chittenden wrote:

> > > Here's a fun one.
> > >
> > > test=# CREATE TABLE table_s1 (i int);
> > > test=# CREATE TABLE table_s2 (j int);
> > > test=# EXPLAIN ANALYZE SELECT table_s1.i, table_s2.j FROM table_s1 AS s1, table_s2 AS s2 WHERE s1.i = s2.j;
> > > NOTICE:  adding missing FROM-clause entry for table "table_s1"
> > > NOTICE:  adding missing FROM-clause entry for table "table_s2"
> > >                                                      QUERY PLAN
> > >
---------------------------------------------------------------------------------------------------------------------
> > >  Nested Loop  (cost=0.00..0.03 rows=1 width=8) (actual time=0.03..0.03 rows=0 loops=1)
> > >    ->  Nested Loop  (cost=0.00..0.02 rows=1 width=4) (actual time=0.02..0.02 rows=0 loops=1)
> > >          ->  Nested Loop  (cost=0.00..0.01 rows=1 width=0) (actual time=0.01..0.01 rows=0 loops=1)
> > >                Join Filter: ("outer".i = "inner".j)
> > >                ->  Seq Scan on table_s1 s1  (cost=0.00..0.00 rows=1 width=4) (actual time=0.01..0.01 rows=0
loops=1)
> > >                ->  Seq Scan on table_s2 s2  (cost=0.00..0.00 rows=1 width=4) (never executed)
> > >          ->  Seq Scan on table_s1  (cost=0.00..0.00 rows=1 width=4) (never executed)
> > >    ->  Seq Scan on table_s2  (cost=0.00..0.00 rows=1 width=4) (never executed)
> > >  Total runtime: 0.20 msec
> > > (9 rows)
> > >
> > > If there's real data in the tables, this joins the tables on itself
> > > and execution times explode, naturally.  I don't know if the spec says
> > > this is the correct behavior or not, but I have a feeling its not and
> > > this is a bug.  -sc
> >
> > Well, the query is technically invalid I think.
>
> I'm not 100% sure what the definition of invalid is...  If I turn off
> add_missing_from, it still fails.  ex:
>
> test=# EXPLAIN ANALYZE SELECT table_s1.i, table_s2.j FROM table_s1 AS s1, table_s2 AS s2 WHERE s1.i = s2.j;
> ERROR:  missing FROM-clause entry for table "table_s1"
>
> I know the docs say, "When an alias is provided, it completely hides
> the actual name of the table or function; for example given FROM foo
> AS f, the remainder of the SELECT must refer to this FROM item as f
> not foo."  It just struck me as a strange behavior.

That's AFAIK the required behavior for SQL (that a table alias hides the
other name for the table) and thus for SQL the query would be malformed
and violate some grammar or syntax rule when it tries to alias a name that
doesn't exist (because table_s1.i or table_s2.j don't resolve to something
out of the FROM list).