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Re: Desc Commnad in pgsql?

From: Christopher Browne <cbbrowne(at)acm(dot)org>
To: pgsql-sql(at)postgresql(dot)org
Subject: Re: Desc Commnad in pgsql?
Date: 2008-04-19 16:55:53
Message-ID: 87skxh3ht2.fsf@wolfe.cbbrowne.com (view raw or flat)
Thread:
Lists: pgsql-sql
The world rejoiced as vikasraigupta(at)gmail(dot)com (VG) wrote:
> Hello All,
> I like to know how can I achieve the same functionality that is give by desc commnad in mysql or oracle.
> Also specify me the book related to pgsql as a beginner.
> Presently my task is going to be communication of ruby with pgsql
> Thanks in advanced.

If you were referring to the usage of "desc" to indicate "descending
order", as in:
   select * from some table order by id desc
well, that's pretty standard SQL usage, and will work much as it
would in MySQL(tm) or Oracle.

If you're looking for ways to "describe" a table, there are two
mechanisms:

  1.  SQL standard (probably SQL:1993) describes an
  "information_schema" which contains tables or views that allow
  querying database metadata in a fairly standard fashion.

  PostgreSQL supports that.

  2.  Probably easier and friendlier, albeit nonportable, is to use
  the psql "\d" command.

  Here's an example:

cbbrowne(at)wolfe:~> psql ledgersmb                                                                                                             Saturday 12:51:13
Welcome to psql 8.1.10, the PostgreSQL interactive terminal.

Type:  \copyright for distribution terms
       \h for help with SQL commands
       \? for help with psql commands
       \g or terminate with semicolon to execute query
       \q to quit

ledgersmb=# \d acc_trans
                                Table "public.acc_trans"
     Column     |  Type   |                          Modifiers                          
----------------+---------+-------------------------------------------------------------
 trans_id       | integer | 
 chart_id       | integer | not null
 transdate      | date    | default date('now'::text)
 source         | text    | 
 cleared        | boolean | default false
 fx_transaction | boolean | default false
 project_id     | integer | 
 memo           | text    | 
 invoice_id     | integer | 
 amount         | numeric | 
 entry_id       | bigint  | not null default nextval('acctrans_entry_id_seq'::regclass)
Indexes:
    "acc_trans_pkey" PRIMARY KEY, btree (entry_id)
    "acc_trans_chart_id_key" btree (chart_id)
    "acc_trans_source_key" btree (lower(source))
    "acc_trans_trans_id_key" btree (trans_id)
    "acc_trans_transdate_key" btree (transdate)
Foreign-key constraints:
    "$1" FOREIGN KEY (chart_id) REFERENCES chart(id)
    "$2" FOREIGN KEY (chart_id) REFERENCES chart(id)
    "$3" FOREIGN KEY (chart_id) REFERENCES chart(id)
    "$4" FOREIGN KEY (chart_id) REFERENCES chart(id)
    "acc_trans_chart_id_fkey" FOREIGN KEY (chart_id) REFERENCES chart(id)

You can query the schemas for all sorts of objects, complete with
tab-completion; type "\?" at the psql prompt to see all of the
internal psql commands.  There is a whole section entitled
"Informational" that shows modifiers to \d to query various sorts of
objects.

For instance:
\dt will list all tables
\ds will list all sequences
\dv will list all views
and there's a further cast of ~20 variants for various different sorts
of objects.
-- 
let name="cbbrowne" and tld="gmail.com" in String.concat "@" [name;tld];;
http://linuxdatabases.info/info/postgresql.html
"Java and C++ make you think that the new ideas are like the old ones.
Java is the most distressing thing to hit computing since MS-DOS."
-- Alan Kay

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