Обсуждение: SQL query: List all the databases in the server

Hi all!

I need SQL analog of \l command from psql.
Something like "list databases".

Does anyone can help me?

Beforehand thank,
Roman.

On Tue, 3 Jul 2001, Roman Smirnov wrote:

> Hi all!
>
> I need SQL analog of \l command from psql.
> Something like "list databases".

If you just want a list of them you can get it from pg_database:

select datname from pg_database;

if you also want the username of the database owner you'll have to
cross pg_database.datdba to pg_user.usesysid something like this:

select d.datname,u.usename from pg_database d, pg_user u where d.datdba = u.usesysid;

Vince.
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Vince Vielhaber <vev@michvhf.com> writes:

>> I need SQL analog of \l command from psql.
>> Something like "list databases".
>
> If you just want a list of them you can get it from pg_database:
>
> select datname from pg_database;
>
> if you also want the username of the database owner [...]

The psql program implements the various \-ed information commands
using SQL, and you can find the actual code by perusing its source
file "describe.c".  In this case, we find that "\l" is:

SELECT pg_database.datname as "Database",
       pg_user.usename as "Owner",
       pg_encoding_to_char(pg_database.encoding) as "Encoding",
       obj_description(pg_database.oid) as "Description"
  FROM pg_database, pg_user
 WHERE pg_database.datdba = pg_user.usesysid
UNION
SELECT pg_database.datname as "Database",
       NULL as "Owner",
       pg_encoding_to_char(pg_database.encoding) as "Encoding",
       obj_description(pg_database.oid) as "Description"
  FROM pg_database
 WHERE pg_database.datdba NOT IN (SELECT usesysid FROM pg_user)
ORDER BY "Database";

However, the "Encoding" bits are only included if the system is
compiled with support for multiple character set encodings, and the
"Description" bits only if the command is given as "\l+", which is a
new one for me -- it's not included in "\?" output.  It seems, from a
little experimentation, that that "+" suffix is available also for the
other "\" commands where it's relevant.  Cool!  :-)

The above SELECT is extensively reformatted from the strings it's
built from in the source file, of course.

-tih
--
The basic difference is this: hackers build things, crackers break them.

Tom Ivar Helbekkmo <tih@kpnQwest.no> writes:
> The above SELECT is extensively reformatted from the strings it's
> built from in the source file, of course.

An even easier way to see what queries psql emits for its backslash
commands is to start psql with -E option, then do the backslash
commands.  This gives me, for example,

regression=# \l
********* QUERY **********
SELECT pg_database.datname as "Database",
       pg_user.usename as "Owner"FROM pg_database, pg_user
WHERE pg_database.datdba = pg_user.usesysid

UNION

SELECT pg_database.datname as "Database",
       NULL as "Owner"FROM pg_database
WHERE pg_database.datdba NOT IN (SELECT usesysid FROM pg_user)
ORDER BY "Database"
**************************

   List of databases
  Database  |  Owner
------------+----------
 regression | postgres
 template0  | postgres
 template1  | postgres
(3 rows)

regression=#

            regards, tom lane

Thanks to all!

Your help was very usefull

Thanks again,
Roman