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<title>1.4.Accessing a Database</title>
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="tutorial-accessdb"></a>1.4.Accessing a Database</h2></div></div></div>
<a name="id567169"></a><p> Once you have created a database, you can access it by:
</p>
<div class="itemizedlist"><ul type="bullet" compact>
<li style="list-style-type: disc"><p> Running the <span class="productname">PostgreSQL</span> interactive
terminal program, called <span class="application"><em class="firstterm">psql</em></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">PgAccess</span> or an office suite with
<acronym class="acronym">ODBC</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" title="PartIV.Client Interfaces">PartIV, “Client Interfaces”</a>.
</p></li>
</ul></div>
<p>
You probably want to start up <code class="command">psql</code>, to try out
the examples in this tutorial. It can be activated for the
<code class="literal">mydb</code> database by typing the command:
</p>
<pre class="screen"><code class="prompt">$</code> <strong class="userinput"><code>psql mydb</code></strong></pre>
<p>
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.
</p>
<p> In <code class="command">psql</code>, you will be greeted with the following
message:
</p>
<pre class="screen">Welcome to psql 8.1.4, 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=></pre>
<p>
<a name="id567298"></a>
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 <span class="productname">PostgreSQL</span>
yourself. Being a superuser means that you are not subject to
access controls. For the purpose of this tutorial this is not of
importance.
</p>
<p> If you encounter problems starting <code class="command">psql</code>
then go back to the previous section. The diagnostics of
<code class="command">createdb</code> and <code class="command">psql</code> are
similar, and if the former worked the latter should work as well.
</p>
<p> The last line printed out by <code class="command">psql</code> is the
prompt, and it indicates that <code class="command">psql</code> is listening
to you and that you can type <acronym class="acronym">SQL</acronym> queries into a
work space maintained by <code class="command">psql</code>. Try out these
commands:
<a name="id567378"></a>
</p>
<pre class="screen"><code class="prompt">mydb=></code> <strong class="userinput"><code>SELECT version();</code></strong>
version
----------------------------------------------------------------
PostgreSQL 8.1.4 on i586-pc-linux-gnu, compiled by GCC 2.96
(1 row)
<code class="prompt">mydb=></code> <strong class="userinput"><code>SELECT current_date;</code></strong>
date
------------
2002-08-31
(1 row)
<code class="prompt">mydb=></code> <strong class="userinput"><code>SELECT 2 + 2;</code></strong>
?column?
----------
4
(1 row)</pre>
<p>
</p>
<p> The <code class="command">psql</code> program has a number of internal
commands that are not SQL commands. They begin with the backslash
character, “<span class="quote"><code class="literal">\</code></span>”. Some of these
commands were listed in the welcome message. 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"><code class="prompt">mydb=></code> <strong class="userinput"><code>\h</code></strong></pre>
<p>
</p>
<p> To get out of <code class="command">psql</code>, type
</p>
<pre class="screen"><code class="prompt">mydb=></code> <strong class="userinput"><code>\q</code></strong></pre>
<p>
and <code class="command">psql</code> will quit and return you to your
command shell. (For more internal commands, type
<code class="literal">\?</code> at the <code class="command">psql</code> prompt.) The
full capabilities of <code class="command">psql</code> are documented in
<a href="app-psql.html" title="psql"><span class="refentrytitle"><a name="app-psql-title"></a><span class="application">psql</span></span></a>. If <span class="productname">PostgreSQL</span> is
installed correctly you can also type <code class="literal">man psql</code>
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.
</p>
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