Thread: LEFT JOIN used in psql describe.c
Does anyone know why so many LEFT JOINs are used in psql/describe.c to join to the pg_namespace table, like here: printfPQExpBuffer(&buf, "SELECT c.oid,\n" " n.nspname,\n" " c.relname\n" "FROM pg_catalog.pg_class c\n" " LEFT JOIN pg_catalog.pg_namespace n ON n.oid = c.relnamespace\n"); processNamePattern(&buf, pattern, false, false, "n.nspname", "c.relname", NULL, "pg_catalog.pg_table_is_visible(c.oid)"); I thought a pg_class row always pointed to a valid pg_namespace row because of our dependency restrictions. -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001+ If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania19073
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 > Does anyone know why so many LEFT JOINs are used in psql/describe.c to > join to the pg_namespace table, like here: > > I thought a pg_class row always pointed to a valid pg_namespace row > because of our dependency restrictions. Yes, pg_relnamespace is definitely not null. I've actually already removed the left joins from my \df patch, since I had to rewrite some of the queries anyway. If this is wrong, please let me know of course! The patch has actually been done for some time now, but the tab completion part of it got tricky with things like \df <tab> and \dfS <tab>, since the code pretty much assumes that the only differentiation of system/non-system objects occurs in pg_class objects. I'll try to get back to it next week, once DBD::Pg 1.41 is finished up. - -- Greg Sabino Mullane greg@turnstep.com PGP Key: 0x14964AC8 200504012315 http://biglumber.com/x/web?pk=2529DF6AB8F79407E94445B4BC9B906714964AC8 -----BEGIN PGP SIGNATURE----- iD8DBQFCThy7vJuQZxSWSsgRAuNRAKClDG8QDxnX7LJMWqODtGqKnClpQQCfaZZ8 UwEpCmHJOyfSOuF0MAkQ7xg= =blNw -----END PGP SIGNATURE-----
"Greg Sabino Mullane" <greg@turnstep.com> writes:
>> Does anyone know why so many LEFT JOINs are used in psql/describe.c to
>> join to the pg_namespace table, like here:
> Yes, pg_relnamespace is definitely not null. I've actually already removed
> the left joins from my \df patch, since I had to rewrite some of the
> queries anyway. If this is wrong, please let me know of course!
I think the idea was to be certain to show every pg_proc entry (or other
catalog for other \d commands), no matter how badly broken the catalog
interrelationships might be. If there's not an unarguable reason
for eliminating the left joins I'd be inclined to keep it like that.
What does an inner join buy here, other than brittleness?
(Yeah, I have the perspective of a developer who deals with broken
situations every day. So?)
regards, tom lane
Tom Lane wrote: > "Greg Sabino Mullane" <greg@turnstep.com> writes: > >> Does anyone know why so many LEFT JOINs are used in psql/describe.c to > >> join to the pg_namespace table, like here: > > > Yes, pg_relnamespace is definitely not null. I've actually already removed > > the left joins from my \df patch, since I had to rewrite some of the > > queries anyway. If this is wrong, please let me know of course! > > I think the idea was to be certain to show every pg_proc entry (or other > catalog for other \d commands), no matter how badly broken the catalog > interrelationships might be. If there's not an unarguable reason > for eliminating the left joins I'd be inclined to keep it like that. > What does an inner join buy here, other than brittleness? > > (Yeah, I have the perspective of a developer who deals with broken > situations every day. So?) If we have problems with the system catalogs, I don't see how this join has a high probability of catching the problem. If there was some known problem of the join not always working, I could see the use of LEFT JOIN, but there isn't, so it just seems confusing, and these queries are used by others as models of how to do system joins, so could confuse our users as well. I think the LEFT JOIN should be removed unless there is a known problem, and if one shows up, we can re-add them later. -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001+ If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania19073
Bruce Momjian wrote: > Tom Lane wrote: > > "Greg Sabino Mullane" <greg@turnstep.com> writes: > > >> Does anyone know why so many LEFT JOINs are used in psql/describe.c to > > >> join to the pg_namespace table, like here: > > > > > Yes, pg_relnamespace is definitely not null. I've actually already removed > > > the left joins from my \df patch, since I had to rewrite some of the > > > queries anyway. If this is wrong, please let me know of course! > > > > I think the idea was to be certain to show every pg_proc entry (or other > > catalog for other \d commands), no matter how badly broken the catalog > > interrelationships might be. If there's not an unarguable reason > > for eliminating the left joins I'd be inclined to keep it like that. > > What does an inner join buy here, other than brittleness? > > > > (Yeah, I have the perspective of a developer who deals with broken > > situations every day. So?) > > If we have problems with the system catalogs, I don't see how this join > has a high probability of catching the problem. If there was some known > problem of the join not always working, I could see the use of LEFT > JOIN, but there isn't, so it just seems confusing, and these queries are > used by others as models of how to do system joins, so could confuse our > users as well. > > I think the LEFT JOIN should be removed unless there is a known problem, > and if one shows up, we can re-add them later. I still think that the LEFT JOINs used in psql system queries is confusing and perhaps adds performance overhead while adding little reliability, but no one else seems to think so so I will drop the idea. -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001+ If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania19073
On Tue, 10 May 2005, Bruce Momjian wrote: > Bruce Momjian wrote: >> Tom Lane wrote: >>> "Greg Sabino Mullane" <greg@turnstep.com> writes: >>>>> Does anyone know why so many LEFT JOINs are used in psql/describe.c to >>>>> join to the pg_namespace table, like here: >>> >>>> Yes, pg_relnamespace is definitely not null. I've actually already removed >>>> the left joins from my \df patch, since I had to rewrite some of the >>>> queries anyway. If this is wrong, please let me know of course! >>> >>> I think the idea was to be certain to show every pg_proc entry (or other >>> catalog for other \d commands), no matter how badly broken the catalog >>> interrelationships might be. If there's not an unarguable reason >>> for eliminating the left joins I'd be inclined to keep it like that. >>> What does an inner join buy here, other than brittleness? >>> >>> (Yeah, I have the perspective of a developer who deals with broken >>> situations every day. So?) >> >> If we have problems with the system catalogs, I don't see how this join >> has a high probability of catching the problem. If there was some known >> problem of the join not always working, I could see the use of LEFT >> JOIN, but there isn't, so it just seems confusing, and these queries are >> used by others as models of how to do system joins, so could confuse our >> users as well. >> >> I think the LEFT JOIN should be removed unless there is a known problem, >> and if one shows up, we can re-add them later. > > I still think that the LEFT JOINs used in psql system queries is > confusing and perhaps adds performance overhead while adding little > reliability, but no one else seems to think so so I will drop the idea. I'm a bit confused here, but I believe Tom (at least how I read it) was agreeing with you about pulling the LEFT JOIN out ... "I think the LEFT JOIN should be removed unless there is a known problem, and if one shows up, we can re-add them later." ... or am I mis-quoting? ---- Marc G. Fournier Hub.Org Networking Services (http://www.hub.org) Email: scrappy@hub.org Yahoo!: yscrappy ICQ: 7615664
Marc G. Fournier wrote: > On Tue, 10 May 2005, Bruce Momjian wrote: > > > Bruce Momjian wrote: > >> Tom Lane wrote: > >>> "Greg Sabino Mullane" <greg@turnstep.com> writes: > >>>>> Does anyone know why so many LEFT JOINs are used in psql/describe.c to > >>>>> join to the pg_namespace table, like here: > >>> > >>>> Yes, pg_relnamespace is definitely not null. I've actually already removed > >>>> the left joins from my \df patch, since I had to rewrite some of the > >>>> queries anyway. If this is wrong, please let me know of course! > >>> > >>> I think the idea was to be certain to show every pg_proc entry (or other > >>> catalog for other \d commands), no matter how badly broken the catalog > >>> interrelationships might be. If there's not an unarguable reason > >>> for eliminating the left joins I'd be inclined to keep it like that. > >>> What does an inner join buy here, other than brittleness? > >>> > >>> (Yeah, I have the perspective of a developer who deals with broken > >>> situations every day. So?) > >> > >> If we have problems with the system catalogs, I don't see how this join > >> has a high probability of catching the problem. If there was some known > >> problem of the join not always working, I could see the use of LEFT > >> JOIN, but there isn't, so it just seems confusing, and these queries are > >> used by others as models of how to do system joins, so could confuse our > >> users as well. > >> > >> I think the LEFT JOIN should be removed unless there is a known problem, > >> and if one shows up, we can re-add them later. > > > > I still think that the LEFT JOINs used in psql system queries is > > confusing and perhaps adds performance overhead while adding little > > reliability, but no one else seems to think so so I will drop the idea. > > I'm a bit confused here, but I believe Tom (at least how I read it) was > agreeing with you about pulling the LEFT JOIN out ... "I think the LEFT > JOIN should be removed unless there is a known problem, and if one shows > up, we can re-add them later." ... or am I mis-quoting? I am actually quoting myself in the posting, so the words are mine, not Tom's. The basic issue is code simplicity vs. robustness, and I am leaning to the former because there is no known robustness problem. It is actually opposite of our opinions on checking for unreferenced files, where I want robustness (because it is a known problem) and Tom wants simplicity (though he is flexible on this), so it seems the two of us switch sides occasionally. :-) -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001+ If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania19073