Hi Roman,

Comments are stored in the system catalog table pg_description. To select a
column comment ("description" in pg_description) you need the specify the
objoid for the table ("relfilenode" from pg_class for the table in question)
and the column number ("objsubid").

test=# select description from pg_description where objoid = 306461 and
objsubid = 0;

description
-----------------------------------
Weight Units~Unit~unitdescription
(1 row)

HTH,
George

----- Original Message -----
From: "A u r k a" <aurka (AT) centrum (DOT) cz>
To: <pgsql-novice (AT) postgresql (DOT) org>
Sent: Thursday, January 15, 2004 9:04 AM
Subject: [NOVICE] How can I select a comment on a column in a query?



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TIP 8: explain analyze is your friend

George Weaver <gweaver (AT) shaw (DOT) ca> writes:
Also, there is a col_description() function that encapsulates this
query. I'd recommend col_description() and its sibling obj_description()
in preference to examining the pg_description catalog directly. See
"Comment Information Functions" in
http://www.postgresql.org/docs/7.4/s...ions-misc.html

Here's a simple example:

regression=# create table mytab (mycol int);
CREATE TABLE
regression=# comment on column mytab.mycol is 'my comment';
COMMENT
regression=# select col_description('mytab'::regclass, 1);
col_description
-----------------
my comment
(1 row)

(I'm using the regclass datatype as a substitute for an explicit
lookup in pg_class to get the OID of the table. This feature is
new since 7.3 or thereabouts.)

regards, tom lane

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