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 pgAdmin or an office suite with ODBC or JDBC 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.
You probably want to start up psql to try
the examples in this tutorial. It can be activated for the
mydb database by typing the command:
$psql mydb
If you do not supply the database name then it will default to your
user account name. You already discovered this scheme in the
previous section using createdb.
In psql, you will be greeted with the following
message:
psql (12.2) Type "help" for help. mydb=>
mydb=#
That would mean you are a database superuser, which is most likely the case if you installed the PostgreSQL instance yourself. Being a superuser means that you are not subject to access controls. For the purposes of this tutorial that is not important.
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 12.2 on x86_64-pc-linux-gnu, compiled by gcc (Debian 4.9.2-10) 4.9.2, 64-bit (1 row)mydb=>SELECT current_date;date ------------ 2016-01-07 (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, “\”.
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. In this tutorial we will not use these
features explicitly, but you can use them yourself when it is helpful.