Re: Series of 10 questions about the use of postgresql, generally.

On Thu, Aug 5, 2021 at 9:46 PM A Z <poweruserm(at)live(dot)com(dot)au> wrote:

>
> 1. Are there free script for CREATE TYPE (native type) or types out
> there, online, free for commercial use? With function support, too? Can
> someone reply with a link or a suggestion?
>
> Look at the PostgreSQL source code, contrib directory, if you want an idea
of how extension types can be added to the system.

>
> 1. If I am using the COPY command for input and output around *.csv
> files, how may I specify internal tuple delimiters of ',', but at the same
> time also specify an end of line delimeter of ';' ?
>
> The COPY command references tells you what is possible. It is not
intended to be particularly flexible, instead focusing on doing one thing
extremely well. The data ecosystem has plenty of tools to convert files
from one format to another.

>> 3. How may I get postgresql to output the create table statement(s) for
one or more tables of one database?

Easiest way, pg_dump:
https://www.postgresql.org/docs/current/app-pgdump.html

psql, and many other "admin" style database client programs also provide a
facility to "show creation command" for a selected object, table or
otherwise. This proves it is possible to also just dive into the catalogs
and system functions to write something yourself - but why re-invent the
wheel.

I'm unaware of an in-server function that provides this, a quick skim in
the obvious place turns up nothing for table creation.
https://www.postgresql.org/docs/current/functions-info.html

> 1. I know that I can use COPY to import or export one database table
> between it and a *.csv file. Can I use it to do this with multiple TABLES
> and *.csv files specified in one COPY COMMAND, or not? How may I use COPY,
> or another default native postgresql function, to export or import create
> table commands to and from a *.csv file?
>
> You should probably extend your consideration for what tooling you will
use beyond native PostgreSQL. Data manipulation technology for
import/export, particularly via CSV, tends to get more attention from the
community than the main project.

> 1. In the absence of OS command line instructions, is there an
> internal postgresql way, via COPY or another function for example, to
> backup an entire database, with all its create table statements and all
> insert statements, and any other associated object, in one hit? Or is this
> ill advised?
>
> If you don't have OS command line capability then you aren't responsible
for the backups - or whatever platform you are using should be supplying
you some alternative.

> 1. -How exactly do Intervals work, via themselves and in relation to
> the other provided native datatypes? What are Intervals used for?
>
> Almost exactly:
https://www.postgresql.org/docs/current/datatype-datetime.html#DATATYPE-INTERVAL-INPUT

You can find "exactly" in the source code, but I would suggest that you
don't really want that level of detail.

As intervals are durations of time they naturally have operators that allow
them to interact with the various datetime types.

https://www.postgresql.org/docs/current/functions-datetime.html

> 1. When setting up communication to remote databases on remote
> machines, I need to use the OPTIONS() function. It seems to require as its
> first function parameter, the schema of the table (the second parameter)
> that it wants to access. Can I supply a null schema, and still be able to
> reference the remote table, or must I also make use of IMPORT FOREIGN
> SCHEMA?
>
> OPTIONS isn't a function, is a clause label, like "SELECT" or "FROM", that
also requires the stuff pertaining to it be surrounding by parentheses,
like "FROM (SELECT 1 FROM tbl) AS tbl1" (FROM is not a function...).

schema_name
This option, which can be specified for a foreign table, gives the schema
name to use for the foreign table on the remote server. If this option is
omitted, the name of the foreign table's schema is used.
https://www.postgresql.org/docs/current/postgres-fdw.html

CREATE FOREIGN TABLE and IMPORT FOREIGN SCHEMA are mutually exclusive ways
to gets foreign table linked into the local database.

If you have additional questions on this topic I would suggest supplying
actual code if possible - your description here omit too much context.

> 1. When I am using INHERITS to setup inheritance between two tables,
> will this mean that all data inserted into the Parent table is
> automatically updated into the Child table(s), or not?
>
> When you are using table inheritance stop and go read this:
https://wiki.postgresql.org/wiki/Don%27t_Do_This#Don.27t_use_table_inheritance

> 1. What does the VARYING keyword do to an applicable type in a create
> table statement? CHARACTER VARYING becomes entirely equivalent to VARCHAR.
> Static, limited types become more dynamic and are unlimited.
>
> "character varying" is the SQL standard data type - it is an atomic
label. PostgreSQL provides "varchar" as an alias. The "varying" is a
keyword but it isn't a thing - it only has to be a keyword because the SQL
Standard makes implementer's lives difficult by allowing spaces in data
type names (I've never actually seen a complaint of this nature, and I
don't do grammar/parser writing, but I imagine this choice isn't popular).

> 1. How may I access the log for the details of a normal table, or
> similar?
>
> The "log" doesn't contain details about permanent objects usually. Maybe
you mis-heard the word "catalog"?
https://www.postgresql.org/docs/current/catalogs.html

David J.