Thread: how to find foreign key details (column, that is)
Hello all,
suppose I know that there are several tables with foreign
keys pointing to
demographics.identity.pk
With the help of pg_constraint I can get a list of *tables*
which hold those foreign keys (schema = demographics, tbl = identity,
col = pk):
select
%(schema)s as referenced_schema,
%(tbl)s as referenced_table,
%(col)s as referenced_column,
conrelid::regclass as foreign_table,
confkey as referenced_column_list
from
pg_constraint
where
contype = 'f'
and
confrelid = (
select oid from pg_class where relname = %(tbl)s and relnamespace = (
select oid from pg_namespace where nspname = %(schema)s
)
) and
(
select attnum
from pg_attribute
where
attrelid = (select oid from pg_class where relname = %(tbl)s and relnamespace = (
select oid from pg_namespace where nspname = %(schema)s
))
and
attname = %(col)s
) = any(confkey)
I cannot, however, for the life of it find out how to learn
the *column* the foreign key is on. IOW I can find out that
clinical.allergy
has a foreign key to
demographics.identity.pk
but I cannot find out that the column representing the
foreign key is
clinical.allergy.fk_identity
How can I go about this ?
Thanks,
Karsten
--
GPG key ID E4071346 @ wwwkeys.pgp.net
E167 67FD A291 2BEA 73BD 4537 78B9 A9F9 E407 1346
Karsten Hilbert <Karsten.Hilbert@gmx.net> writes:
> I cannot, however, for the life of it find out how to learn
> the *column* the foreign key is on.
pg_constraint.conkey has the referencing columns' numbers.
regards, tom lane
On Sun, Dec 14, 2008 at 02:37:51PM -0500, Tom Lane wrote: > Subject: Re: [GENERAL] how to find foreign key details (column, that is) > > Karsten Hilbert <Karsten.Hilbert@gmx.net> writes: > > I cannot, however, for the life of it find out how to learn > > the *column* the foreign key is on. > > pg_constraint.conkey has the referencing columns' numbers. Tom, thanks, as usual awesome support on the 3rd Sunday in Advent ... This is what my 8.3 manual says: conkey │ int2[] │ pg_attribute.attnum │ If a table constraint, list of columns which the constraint constrains │ From that I wouldn't have figured it'd apply to foreign keys as well. So I assume it is fair to say that "foreign keys are one type of table constraint", right ? Thanks again, Karsten -- GPG key ID E4071346 @ wwwkeys.pgp.net E167 67FD A291 2BEA 73BD 4537 78B9 A9F9 E407 1346
Karsten Hilbert <Karsten.Hilbert@gmx.net> writes:
> This is what my 8.3 manual says:
> conkey │ int2[] │ pg_attribute.attnum │ If a table constraint, list of columns which the constraint constrains │
> From that I wouldn't have figured it'd apply to foreign keys
> as well. So I assume it is fair to say that "foreign keys
> are one type of table constraint", right ?
Right. I think what the comment is actually trying to point out is that
conkey isn't relevant to domain constraints, which also appear in
pg_constraint.
regards, tom lane
Tom Lane wrote:
> Karsten Hilbert <Karsten.Hilbert@gmx.net> writes:
> > This is what my 8.3 manual says:
>
> > conkey │ int2[] │ pg_attribute.attnum │ If a table constraint, list of columns which the constraint constrains │
>
> > From that I wouldn't have figured it'd apply to foreign keys
> > as well. So I assume it is fair to say that "foreign keys
> > are one type of table constraint", right ?
>
> Right. I think what the comment is actually trying to point out is that
> conkey isn't relevant to domain constraints, which also appear in
> pg_constraint.
Can someone come up with better documention wording for conkey? I
can't:
http://developer.postgresql.org/pgdocs/postgres/catalog-pg-constraint.html
--
Bruce Momjian <bruce@momjian.us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ If your life is a hard drive, Christ can be your backup. +
On Wed, Jan 21, 2009 at 01:49:44PM -0500, Bruce Momjian wrote: > Tom Lane wrote: > > Karsten Hilbert <Karsten.Hilbert@gmx.net> writes: > > > This is what my 8.3 manual says: > > > > > conkey │ int2[] │ pg_attribute.attnum │ If a table constraint, list of columns which the constraint constrains │ > > > > > From that I wouldn't have figured it'd apply to foreign keys > > > as well. So I assume it is fair to say that "foreign keys > > > are one type of table constraint", right ? > > > > Right. I think what the comment is actually trying to point out is that > > conkey isn't relevant to domain constraints, which also appear in > > pg_constraint. > > Can someone come up with better documention wording for conkey? I > can't: > > http://developer.postgresql.org/pgdocs/postgres/catalog-pg-constraint.html How about adding a second line: "Note: since foreign keys are table constraints, applies to those, too." or "If a foreign key, list of columns referencing the target table" (note, "referencing" as opposed to "referenced by" as in confkey) Karsten -- GPG key ID E4071346 @ wwwkeys.pgp.net E167 67FD A291 2BEA 73BD 4537 78B9 A9F9 E407 1346
Karsten Hilbert wrote: > On Wed, Jan 21, 2009 at 01:49:44PM -0500, Bruce Momjian wrote: > > > Tom Lane wrote: > > > Karsten Hilbert <Karsten.Hilbert@gmx.net> writes: > > > > This is what my 8.3 manual says: > > > > > > > conkey ? int2[] ? pg_attribute.attnum ? If a table constraint, list of columns which the constraint constrains ? > > > > > > > From that I wouldn't have figured it'd apply to foreign keys > > > > as well. So I assume it is fair to say that "foreign keys > > > > are one type of table constraint", right ? > > > > > > Right. I think what the comment is actually trying to point out is that > > > conkey isn't relevant to domain constraints, which also appear in > > > pg_constraint. > > > > Can someone come up with better documentation wording for conkey? I > > can't: > > > > http://developer.postgresql.org/pgdocs/postgres/catalog-pg-constraint.html > > How about adding a second line: > > "Note: since foreign keys are table constraints, applies to those, too." > > or > > "If a foreign key, list of columns referencing the target table" > > (note, "referencing" as opposed to "referenced by" as in confkey) I went a different direction with the documentation; I simplified the wording and made it more explicit; attached and applied. -- Bruce Momjian <bruce@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + If your life is a hard drive, Christ can be your backup. + Index: doc/src/sgml/catalogs.sgml =================================================================== RCS file: /cvsroot/pgsql/doc/src/sgml/catalogs.sgml,v retrieving revision 2.194 diff -c -c -r2.194 catalogs.sgml *** doc/src/sgml/catalogs.sgml 4 Feb 2009 21:30:41 -0000 2.194 --- doc/src/sgml/catalogs.sgml 7 Feb 2009 14:52:38 -0000 *************** *** 1983,1989 **** <entry><structfield>conkey</structfield></entry> <entry><type>int2[]</type></entry> <entry><literal><link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.attnum</></entry> ! <entry>If a table constraint, list of columns which the constraint constrains</entry> </row> <row> --- 1983,1989 ---- <entry><structfield>conkey</structfield></entry> <entry><type>int2[]</type></entry> <entry><literal><link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.attnum</></entry> ! <entry>If a table constraint (including a foreign key), list of the constrained columns</entry> </row> <row>