PostgreSQL "DESCRIBE TABLE" – Dev

The best answers to the question “PostgreSQL "DESCRIBE TABLE"” in the category Dev.

QUESTION:

How do you perform the equivalent of Oracle’s DESCRIBE TABLE in PostgreSQL (using the psql command)?

ANSWER:

In addition to the PostgreSQL way (\d ‘something’ or \dt ‘table’ or \ds ‘sequence’ and so on)

The SQL standard way, as shown here:

select column_name, data_type, character_maximum_length, column_default, is_nullable
from INFORMATION_SCHEMA.COLUMNS where table_name="<name of table>";

It’s supported by many db engines.

ANSWER:

Try this (in the psql command-line tool):

\d+ tablename

See the manual for more info.

ANSWER:

You can do that with a psql slash command:

 \d myTable describe table

It also works for other objects:

 \d myView describe view
 \d myIndex describe index
 \d mySequence describe sequence

Source: faqs.org

ANSWER:

If you want to obtain it from query instead of psql, you can query the catalog schema. Here’s a complex query that does that:

SELECT  
    f.attnum AS number,  
    f.attname AS name,  
    f.attnum,  
    f.attnotnull AS notnull,  
    pg_catalog.format_type(f.atttypid,f.atttypmod) AS type,  
    CASE  
        WHEN p.contype="p" THEN 't'  
        ELSE 'f'  
    END AS primarykey,  
    CASE  
        WHEN p.contype="u" THEN 't'  
        ELSE 'f'
    END AS uniquekey,
    CASE
        WHEN p.contype="f" THEN g.relname
    END AS foreignkey,
    CASE
        WHEN p.contype="f" THEN p.confkey
    END AS foreignkey_fieldnum,
    CASE
        WHEN p.contype="f" THEN g.relname
    END AS foreignkey,
    CASE
        WHEN p.contype="f" THEN p.conkey
    END AS foreignkey_connnum,
    CASE
        WHEN f.atthasdef="t" THEN d.adsrc
    END AS default
FROM pg_attribute f  
    JOIN pg_class c ON c.oid = f.attrelid  
    JOIN pg_type t ON t.oid = f.atttypid  
    LEFT JOIN pg_attrdef d ON d.adrelid = c.oid AND d.adnum = f.attnum  
    LEFT JOIN pg_namespace n ON n.oid = c.relnamespace  
    LEFT JOIN pg_constraint p ON p.conrelid = c.oid AND f.attnum = ANY (p.conkey)  
    LEFT JOIN pg_class AS g ON p.confrelid = g.oid  
WHERE c.relkind = 'r'::char  
    AND n.nspname="%s"  -- Replace with Schema name  
    AND c.relname="%s"  -- Replace with table name  
    AND f.attnum > 0 ORDER BY number
;

It’s pretty complex but it does show you the power and flexibility of the PostgreSQL system catalog and should get you on your way to pg_catalog mastery ;-). Be sure to change out the %s’s in the query. The first is Schema and the second is the table name.