Finding the primary key of tables

On 08/03/10 12:13 PM, George Silva wrote:

Hello guys,

I'm building a function which needs to know what is the primary key of
a certain table (all in pgplsql).

I was using select * from information_schema.key_column_usage where
table_schema='foo' and table_name = 'aaa'; but that will give me
multiple results in case of additional keys in the table.

the primary key index is called tablename_pkey ... afaik, this is the
only thing that makes it special, otherwise, its just another index with
a unique constraint.

On Tue, Aug 3, 2010 at 3:13 PM, George Silva <georger.silva@gmail.com> wrote:

Hello guys,

I'm building a function which needs to know what is the primary key of a
certain table (all in pgplsql).

I was using select * from information_schema.key_column_usage where
table_schema='foo' and table_name = 'aaa'; but that will give me multiple
results in case of additional keys in the table.

Any suggestions?

take a look at information_schema.table_constraint and match on constraint_name.

merlin

On Tue, 2010-08-03 at 16:13 -0300, George Silva wrote:

I'm building a function which needs to know what is the primary key of
a
certain table (all in pgplsql).

I was using select * from information_schema.key_column_usage where
table_schema='foo' and table_name = 'aaa'; but that will give me
multiple
results in case of additional keys in the table.

Any suggestions?

See pg_index.indisprimary column. If it is true, then the it is the PK
of given table.

Regards,
--
Devrim GÜNDÜZ
PostgreSQL Danışmanı/Consultant, Red Hat Certified Engineer
PostgreSQL RPM Repository: http://yum.pgrpms.org
Community: devrim~PostgreSQL.org, devrim.gunduz~linux.org.tr
http://www.gunduz.org Twitter: http://twitter.com/devrimgunduz

I'm going for Merlin's solution. Its the easiest one :P

But I'm also having a problem:

SELECT column_name FROM information_schema.key_column_usage k
LEFT OUTER JOIN information_schema.table_constraints ON (k.table_name =
table_constraints.table_name)
WHERE
table_constraints.constraint_type = 'PRIMARY KEY'
AND k.table_name = 'acidentes'
AND k.table_schema = 'public'

this still returns me multiple columns. Did I forgot something?

2010/8/3 Devrim GÜNDÜZ <devrim@gunduz.org>

On Tue, 2010-08-03 at 16:13 -0300, George Silva wrote:

I'm building a function which needs to know what is the primary key of
a
certain table (all in pgplsql).

I was using select * from information_schema.key_column_usage where
table_schema='foo' and table_name = 'aaa'; but that will give me
multiple
results in case of additional keys in the table.

Any suggestions?

See pg_index.indisprimary column. If it is true, then the it is the PK
of given table.

Regards,
--
Devrim GÜNDÜZ
PostgreSQL Danışmanı/Consultant, Red Hat Certified Engineer
PostgreSQL RPM Repository: http://yum.pgrpms.org
Community: devrim~PostgreSQL.org, devrim.gunduz~linux.org.tr
http://www.gunduz.org Twitter: http://twitter.com/devrimgunduz

--
George R. C. Silva

Desenvolvimento em GIS
http://blog.geoprocessamento.net

2010/8/3 George Silva <georger.silva@gmail.com>:

I'm going for Merlin's solution. Its the easiest one :P

But I'm also having a problem:

SELECT column_name FROM information_schema.key_column_usage k
    LEFT OUTER JOIN information_schema.table_constraints ON (k.table_name =
table_constraints.table_name)
WHERE
        table_constraints.constraint_type = 'PRIMARY KEY'
        AND k.table_name = 'acidentes'
        AND k.table_schema = 'public'

this still returns me multiple columns. Did I forgot something?

yup -- you are supposed be matching on constraint_name, not just
table_name. try:
SELECT column_name FROM information_schema.key_column_usage k
LEFT OUTER JOIN information_schema.table_constraints USING
(table_schema, table_name, constraint_name)
WHERE
table_constraints.constraint_type = 'PRIMARY KEY'
AND k.table_name = 'acidentes'
AND k.table_schema = 'public'

merlin

Thanks a million. Rusty SQL :P

2010/8/3 Merlin Moncure <mmoncure@gmail.com>

2010/8/3 George Silva <georger.silva@gmail.com>:

I'm going for Merlin's solution. Its the easiest one :P

But I'm also having a problem:

SELECT column_name FROM information_schema.key_column_usage k
LEFT OUTER JOIN information_schema.table_constraints ON (k.table_name

=

table_constraints.table_name)
WHERE
table_constraints.constraint_type = 'PRIMARY KEY'
AND k.table_name = 'acidentes'
AND k.table_schema = 'public'

this still returns me multiple columns. Did I forgot something?

yup -- you are supposed be matching on constraint_name, not just
table_name. try:
SELECT column_name FROM information_schema.key_column_usage k
LEFT OUTER JOIN information_schema.table_constraints USING
(table_schema, table_name, constraint_name)
WHERE
table_constraints.constraint_type = 'PRIMARY KEY'
AND k.table_name = 'acidentes'
AND k.table_schema = 'public'

merlin

--
George R. C. Silva

Desenvolvimento em GIS
http://blog.geoprocessamento.net