Retrieving Comments from a PostgreSQL DB

Question

I\'m running a project on a Postgres database and need to retrieve the comments on columns within the DB to be used as table headings and such. I have seen that there are a

Answer 1

Just to be here if somebody will need it.

There are many answers here, but none of them was as simple as I would like it to be. So, based on previous answers and current postgres 9.4, I have created this query:

SELECT 
    obj_description(format('%s.%s',isc.table_schema,isc.table_name)::regclass::oid, 'pg_class') as table_description,
    pg_catalog.col_description(format('%s.%s',isc.table_schema,isc.table_name)::regclass::oid,isc.ordinal_position) as column_description
FROM
    information_schema.columns isc

It fetches table and column descriptions, without any confusing joins and ugly string concatenations.

Answer 2

A slight change to one of the other answers which only gives you columns that have comments on them, this gives you all columns whether they have a comment or not.

select c.table_schema, st.relname as TableName, c.column_name, 
pgd.description
from pg_catalog.pg_statio_all_tables as st
inner join information_schema.columns c
on c.table_schema = st.schemaname
and c.table_name = st.relname
left join pg_catalog.pg_description pgd
on pgd.objoid=st.relid
and pgd.objsubid=c.ordinal_position
where st.relname = 'YourTableName';

Answer 3

It all works by oid,

mat=> SELECT c.oid FROM pg_catalog.pg_class c WHERE c.relname = 'customers';
  oid  
-------
 23208
(1 row)

Now, I have the oid for that table, so I can ask :

mat=> select pg_catalog.obj_description(23208);
  obj_description  
-------------------
 Customers
(1 row)

Then, I can ask for the description of the fourth column :

mat=> select pg_catalog.col_description(23208,4);
             col_description             
-----------------------------------------
 Customer codes, CHS, FACTPOST, POWER...
(1 row)

If you want to know which queries does psql run when you do \dt+ or \d+ customers, just run it with -E.

Answer 4

This works for me using the PostBooks 3.2.2 DB:

select cols.column_name,
(select pg_catalog.obj_description(oid) from pg_catalog.pg_class c where c.relname=cols.table_name) as table_comment
,(select pg_catalog.col_description(oid,cols.ordinal_position::int) from pg_catalog.pg_class c where c.relname=cols.table_name) as column_comment
from information_schema.columns cols
where cols.table_catalog='postbooks' and cols.table_name='apapply'

Regards, Sylnsr

Answer 5

Take care with schemas, this code considers them:

SELECT
    cols.column_name, (
        SELECT
            pg_catalog.col_description(c.oid, cols.ordinal_position::int)
        FROM
            pg_catalog.pg_class c
        WHERE
            c.oid = (SELECT ('"' || cols.table_name || '"')::regclass::oid)
            AND c.relname = cols.table_name
    ) AS column_comment
FROM
    information_schema.columns cols
WHERE
    cols.table_catalog    = 'your_database'
    AND cols.table_name   = 'your_table'
    AND cols.table_schema = 'your_schema';

References:

• Postgresql Document Table and Column Description Comments on Table and Column

• Determining the OID of a table in Postgres 9.1?

Answer 6

I asked a similar question about Postgresql comments last month. If you dig through that, you'll come across some Perl code over on my blog that automates the process of extracting a comment.

To pull out the column names of a table, you can use something like the following:

select
     a.attname  as "colname"
    ,a.attrelid as "tableoid"
    ,a.attnum   as "columnoid"
from
    pg_catalog.pg_attribute a
    inner join pg_catalog.pg_class c on a.attrelid = c.oid
where
        c.relname = 'mytable' -- better to use a placeholder
    and a.attnum > 0
    and a.attisdropped is false
    and pg_catalog.pg_table_is_visible(c.oid)
order by a.attnum

You can then use the tableoid,columnoid tuple to extract the comment of each column (see my question).