Re: List user databases

On 11/9/22 20:57, Ian Lawrence Barwick wrote:
> 2022年11月10日(木) 13:41 Igor Korot <ikorot01(at)gmail(dot)com>:
>>
>> Hi, ALL,
>> According to https://chartio.com/resources/tutorials/how-to-list-databases-and-tables-in-postgresql-using-psql/,
>> there are generally 3 system DBs.
>>
>> However I'm confused with the word general.
>> How many system databases can be made on a PG server?
>
> template0 and template1 are the mandatory system databases which
> cannot be dropped.

Actually that is not strictly true:

https://www.postgresql.org/docs/current/manage-ag-templatedbs.html

"
Note

template1 and template0 do not have any special status beyond the fact
that the name template1 is the default source database name for CREATE
DATABASE. For example, one could drop template1 and recreate it from
template0 without any ill effects. This course of action might be
advisable if one has carelessly added a bunch of junk in template1. (To
delete template1, it must have pg_database.datistemplate = false.)

The postgres database is also created when a database cluster is
initialized. This database is meant as a default database for users and
applications to connect to. It is simply a copy of template1 and can be
dropped and recreated if necessary.
"

>
> "postgres" is created by default for operational convenience, but is
> not essential and can
> be removed if you really want to.
>
> Regards
>
> Ian Barwick
>
>

--
Adrian Klaver
adrian(dot)klaver(at)aklaver(dot)com