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><A
NAME="TUTORIAL-ACCESSDB"
>1.4. Accessing a Database</A
></H1
><P
> Once you have created a database, you can access it by:
<P
></P
></P><UL
COMPACT="COMPACT"
><LI
STYLE="list-style-type: disc"
><P
> Running the <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> interactive
terminal program, called <SPAN
CLASS="APPLICATION"
><I
CLASS="FIRSTTERM"
>psql</I
></SPAN
>, which allows you
to interactively enter, edit, and execute
<ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> commands.
</P
></LI
><LI
STYLE="list-style-type: disc"
><P
> Using an existing graphical frontend tool like
<SPAN
CLASS="APPLICATION"
>pgAdmin</SPAN
> or an office suite with
<ACRONYM
CLASS="ACRONYM"
>ODBC</ACRONYM
> or <ACRONYM
CLASS="ACRONYM"
>JDBC</ACRONYM
> support to create and manipulate a
database. These possibilities are not covered in this
tutorial.
</P
></LI
><LI
STYLE="list-style-type: disc"
><P
> Writing a custom application, using one of the several
available language bindings. These possibilities are discussed
further in <A
HREF="client-interfaces.html"
>Part IV</A
>.
</P
></LI
></UL
><P>
You probably want to start up <TT
CLASS="COMMAND"
>psql</TT
> to try
the examples in this tutorial. It can be activated for the
<TT
CLASS="LITERAL"
>mydb</TT
> database by typing the command:
</P><PRE
CLASS="SCREEN"
><SAMP
CLASS="PROMPT"
>$</SAMP
> <KBD
CLASS="USERINPUT"
>psql mydb</KBD
></PRE
><P>
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 <TT
CLASS="COMMAND"
>createdb</TT
>.
</P
><P
> In <TT
CLASS="COMMAND"
>psql</TT
>, you will be greeted with the following
message:
</P><PRE
CLASS="SCREEN"
>psql (9.2.24)
Type "help" for help.
mydb=></PRE
><P>
The last line could also be:
</P><PRE
CLASS="SCREEN"
>mydb=#</PRE
><P>
That would mean you are a database superuser, which is most likely
the case if you installed the <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> instance
yourself. Being a superuser means that you are not subject to
access controls. For the purposes of this tutorial that is not
important.
</P
><P
> If you encounter problems starting <TT
CLASS="COMMAND"
>psql</TT
>
then go back to the previous section. The diagnostics of
<TT
CLASS="COMMAND"
>createdb</TT
> and <TT
CLASS="COMMAND"
>psql</TT
> are
similar, and if the former worked the latter should work as well.
</P
><P
> The last line printed out by <TT
CLASS="COMMAND"
>psql</TT
> is the
prompt, and it indicates that <TT
CLASS="COMMAND"
>psql</TT
> is listening
to you and that you can type <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> queries into a
work space maintained by <TT
CLASS="COMMAND"
>psql</TT
>. Try out these
commands:
</P><PRE
CLASS="SCREEN"
><SAMP
CLASS="PROMPT"
>mydb=></SAMP
> <KBD
CLASS="USERINPUT"
>SELECT version();</KBD
>
version
-----------------------------------------------------------------------
PostgreSQL 9.2.24 on i586-pc-linux-gnu, compiled by GCC 2.96, 32-bit
(1 row)
<SAMP
CLASS="PROMPT"
>mydb=></SAMP
> <KBD
CLASS="USERINPUT"
>SELECT current_date;</KBD
>
date
------------
2002-08-31
(1 row)
<SAMP
CLASS="PROMPT"
>mydb=></SAMP
> <KBD
CLASS="USERINPUT"
>SELECT 2 + 2;</KBD
>
?column?
----------
4
(1 row)</PRE
><P>
</P
><P
> The <TT
CLASS="COMMAND"
>psql</TT
> program has a number of internal
commands that are not SQL commands. They begin with the backslash
character, <SPAN
CLASS="QUOTE"
>"<TT
CLASS="LITERAL"
>\</TT
>"</SPAN
>.
For example,
you can get help on the syntax of various
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
>
commands by typing:
</P><PRE
CLASS="SCREEN"
><SAMP
CLASS="PROMPT"
>mydb=></SAMP
> <KBD
CLASS="USERINPUT"
>\h</KBD
></PRE
><P>
</P
><P
> To get out of <TT
CLASS="COMMAND"
>psql</TT
>, type:
</P><PRE
CLASS="SCREEN"
><SAMP
CLASS="PROMPT"
>mydb=></SAMP
> <KBD
CLASS="USERINPUT"
>\q</KBD
></PRE
><P>
and <TT
CLASS="COMMAND"
>psql</TT
> will quit and return you to your
command shell. (For more internal commands, type
<TT
CLASS="LITERAL"
>\?</TT
> at the <TT
CLASS="COMMAND"
>psql</TT
> prompt.) The
full capabilities of <TT
CLASS="COMMAND"
>psql</TT
> are documented in
<A
HREF="app-psql.html"
><SPAN
CLASS="APPLICATION"
>psql</SPAN
></A
>. In this tutorial we will not use these
features explicitly, but you can use them yourself when it is helpful.
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