Once you have created a database, you can access it by:
Running the PostgreSQL interactive terminal program, called psql, which allows you to interactively enter, edit, and execute SQL commands.
Using an existing graphical frontend tool like PgAccess or an office suite with ODBC support to create and manipulate a database. These possibilities are not covered in this tutorial.
Writing a custom application, using one of the several available language bindings. These possibilities are discussed further in Part IV, “Client Interfaces”.
You probably want to start up psql
, to try out
the examples in this tutorial. It can be activated for the
mydb
database by typing the command:
$
psql mydb
If you leave off the database name then it will default to your user account name. You already discovered this scheme in the previous section.
In psql
, you will be greeted with the following
message:
Welcome to psql 8.2.3, 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 mydb=>
mydb=#
That would mean you are a database superuser, which is most likely the case if you installed PostgreSQL yourself. Being a superuser means that you are not subject to access controls. For the purposes of this tutorial that is not of importance.
If you encounter problems starting psql
then go back to the previous section. The diagnostics of
createdb
and psql
are
similar, and if the former worked the latter should work as well.
The last line printed out by psql
is the
prompt, and it indicates that psql
is listening
to you and that you can type SQL queries into a
work space maintained by psql
. Try out these
commands:
mydb=>
SELECT version();
version ---------------------------------------------------------------- PostgreSQL 8.2.3 on i586-pc-linux-gnu, compiled by GCC 2.96 (1 row)mydb=>
SELECT current_date;
date ------------ 2002-08-31 (1 row)mydb=>
SELECT 2 + 2;
?column? ---------- 4 (1 row)
The psql
program has a number of internal
commands that are not SQL commands. They begin with the backslash
character, “\
”. Some of these
commands were listed in the welcome message. For example,
you can get help on the syntax of various
PostgreSQL SQL
commands by typing:
mydb=>
\h
To get out of psql
, type
mydb=>
\q
and psql
will quit and return you to your
command shell. (For more internal commands, type
\?
at the psql
prompt.) The
full capabilities of psql
are documented in
psql. If PostgreSQL is
installed correctly you can also type man psql
at the operating system shell prompt to see the documentation. In
this tutorial we will not use these features explicitly, but you
can use them yourself when you see fit.