410 lines
15 KiB
Plaintext
410 lines
15 KiB
Plaintext
<!-- doc/src/sgml/start.sgml -->
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<chapter id="tutorial-start">
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<title>Getting Started</title>
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<sect1 id="tutorial-install">
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<title>Installation</title>
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<para>
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Before you can use <productname>PostgreSQL</productname> you need
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to install it, of course. It is possible that
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<productname>PostgreSQL</productname> is already installed at your
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site, either because it was included in your operating system
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distribution or because the system administrator already installed
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it. If that is the case, you should obtain information from the
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operating system documentation or your system administrator about
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how to access <productname>PostgreSQL</productname>.
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</para>
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<para>
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If you are not sure whether <productname>PostgreSQL</productname>
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is already available or whether you can use it for your
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experimentation then you can install it yourself. Doing so is not
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hard and it can be a good exercise.
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<productname>PostgreSQL</productname> can be installed by any
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unprivileged user; no superuser (<systemitem>root</systemitem>)
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access is required.
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</para>
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<para>
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If you are installing <productname>PostgreSQL</productname>
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yourself, then refer to <xref linkend="installation"/>
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for instructions on installation, and return to
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this guide when the installation is complete. Be sure to follow
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closely the section about setting up the appropriate environment
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variables.
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</para>
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<para>
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If your site administrator has not set things up in the default
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way, you might have some more work to do. For example, if the
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database server machine is a remote machine, you will need to set
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the <envar>PGHOST</envar> environment variable to the name of the
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database server machine. The environment variable
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<envar>PGPORT</envar> might also have to be set. The bottom line is
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this: if you try to start an application program and it complains
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that it cannot connect to the database, you should consult your
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site administrator or, if that is you, the documentation to make
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sure that your environment is properly set up. If you did not
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understand the preceding paragraph then read the next section.
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</para>
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</sect1>
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<sect1 id="tutorial-arch">
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<title>Architectural Fundamentals</title>
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<para>
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Before we proceed, you should understand the basic
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<productname>PostgreSQL</productname> system architecture.
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Understanding how the parts of
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<productname>PostgreSQL</productname> interact will make this
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chapter somewhat clearer.
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</para>
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<para>
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In database jargon, <productname>PostgreSQL</productname> uses a
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client/server model. A <productname>PostgreSQL</productname>
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session consists of the following cooperating processes
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(programs):
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<itemizedlist>
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<listitem>
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<para>
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A server process, which manages the database files, accepts
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connections to the database from client applications, and
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performs database actions on behalf of the clients. The
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database server program is called
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<filename>postgres</filename>.
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<indexterm><primary>postgres</primary></indexterm>
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</para>
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</listitem>
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<listitem>
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<para>
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The user's client (frontend) application that wants to perform
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database operations. Client applications can be very diverse
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in nature: a client could be a text-oriented tool, a graphical
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application, a web server that accesses the database to
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display web pages, or a specialized database maintenance tool.
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Some client applications are supplied with the
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<productname>PostgreSQL</productname> distribution; most are
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developed by users.
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</para>
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</listitem>
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</itemizedlist>
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</para>
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<para>
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As is typical of client/server applications, the client and the
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server can be on different hosts. In that case they communicate
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over a TCP/IP network connection. You should keep this in mind,
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because the files that can be accessed on a client machine might
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not be accessible (or might only be accessible using a different
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file name) on the database server machine.
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</para>
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<para>
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The <productname>PostgreSQL</productname> server can handle
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multiple concurrent connections from clients. To achieve this it
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starts (<quote>forks</quote>) a new process for each connection.
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From that point on, the client and the new server process
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communicate without intervention by the original
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<filename>postgres</filename> process. Thus, the
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supervisor server process is always running, waiting for
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client connections, whereas client and associated server processes
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come and go. (All of this is of course invisible to the user. We
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only mention it here for completeness.)
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</para>
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</sect1>
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<sect1 id="tutorial-createdb">
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<title>Creating a Database</title>
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<indexterm zone="tutorial-createdb">
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<primary>database</primary>
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<secondary>creating</secondary>
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</indexterm>
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<indexterm zone="tutorial-createdb">
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<primary>createdb</primary>
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</indexterm>
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<para>
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The first test to see whether you can access the database server
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is to try to create a database. A running
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<productname>PostgreSQL</productname> server can manage many
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databases. Typically, a separate database is used for each
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project or for each user.
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</para>
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<para>
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Possibly, your site administrator has already created a database
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for your use. In that case you can omit this step and skip ahead
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to the next section.
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</para>
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<para>
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To create a new database, in this example named
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<literal>mydb</literal>, you use the following command:
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<screen>
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<prompt>$</prompt> <userinput>createdb mydb</userinput>
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</screen>
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If this produces no response then this step was successful and you can skip over the
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remainder of this section.
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</para>
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<para>
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If you see a message similar to:
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<screen>
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createdb: command not found
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</screen>
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then <productname>PostgreSQL</productname> was not installed properly. Either it was not
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installed at all or your shell's search path was not set to include it.
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Try calling the command with an absolute path instead:
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<screen>
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<prompt>$</prompt> <userinput>/usr/local/pgsql/bin/createdb mydb</userinput>
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</screen>
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The path at your site might be different. Contact your site
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administrator or check the installation instructions to
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correct the situation.
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</para>
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<para>
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Another response could be this:
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<screen>
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createdb: error: connection to server on socket "/tmp/.s.PGSQL.5432" failed: No such file or directory
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Is the server running locally and accepting connections on that socket?
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</screen>
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This means that the server was not started, or it is not listening
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where <command>createdb</command> expects to contact it. Again, check the
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installation instructions or consult the administrator.
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</para>
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<para>
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Another response could be this:
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<screen>
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createdb: error: connection to server on socket "/tmp/.s.PGSQL.5432" failed: FATAL: role "joe" does not exist
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</screen>
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where your own login name is mentioned. This will happen if the
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administrator has not created a <productname>PostgreSQL</productname> user account
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for you. (<productname>PostgreSQL</productname> user accounts are distinct from
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operating system user accounts.) If you are the administrator, see
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<xref linkend="user-manag"/> for help creating accounts. You will need to
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become the operating system user under which <productname>PostgreSQL</productname>
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was installed (usually <literal>postgres</literal>) to create the first user
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account. It could also be that you were assigned a
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<productname>PostgreSQL</productname> user name that is different from your
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operating system user name; in that case you need to use the <option>-U</option>
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switch or set the <envar>PGUSER</envar> environment variable to specify your
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<productname>PostgreSQL</productname> user name.
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</para>
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<para>
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If you have a user account but it does not have the privileges required to
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create a database, you will see the following:
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<screen>
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createdb: error: database creation failed: ERROR: permission denied to create database
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</screen>
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Not every user has authorization to create new databases. If
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<productname>PostgreSQL</productname> refuses to create databases
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for you then the site administrator needs to grant you permission
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to create databases. Consult your site administrator if this
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occurs. If you installed <productname>PostgreSQL</productname>
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yourself then you should log in for the purposes of this tutorial
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under the user account that you started the server as.
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<footnote>
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<para>
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As an explanation for why this works:
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<productname>PostgreSQL</productname> user names are separate
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from operating system user accounts. When you connect to a
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database, you can choose what
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<productname>PostgreSQL</productname> user name to connect as;
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if you don't, it will default to the same name as your current
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operating system account. As it happens, there will always be a
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<productname>PostgreSQL</productname> user account that has the
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same name as the operating system user that started the server,
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and it also happens that that user always has permission to
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create databases. Instead of logging in as that user you can
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also specify the <option>-U</option> option everywhere to select
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a <productname>PostgreSQL</productname> user name to connect as.
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</para>
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</footnote>
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</para>
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<para>
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You can also create databases with other names.
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<productname>PostgreSQL</productname> allows you to create any
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number of databases at a given site. Database names must have an
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alphabetic first character and are limited to 63 bytes in
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length. A convenient choice is to create a database with the same
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name as your current user name. Many tools assume that database
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name as the default, so it can save you some typing. To create
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that database, simply type:
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<screen>
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<prompt>$</prompt> <userinput>createdb</userinput>
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</screen>
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</para>
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<para>
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If you do not want to use your database anymore you can remove it.
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For example, if you are the owner (creator) of the database
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<literal>mydb</literal>, you can destroy it using the following
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command:
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<screen>
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<prompt>$</prompt> <userinput>dropdb mydb</userinput>
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</screen>
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(For this command, the database name does not default to the user
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account name. You always need to specify it.) This action
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physically removes all files associated with the database and
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cannot be undone, so this should only be done with a great deal of
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forethought.
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</para>
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<para>
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More about <command>createdb</command> and <command>dropdb</command> can
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be found in <xref linkend="app-createdb"/> and <xref linkend="app-dropdb"/>
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respectively.
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</para>
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</sect1>
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<sect1 id="tutorial-accessdb">
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<title>Accessing a Database</title>
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<indexterm zone="tutorial-accessdb">
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<primary>psql</primary>
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</indexterm>
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<para>
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Once you have created a database, you can access it by:
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<itemizedlist spacing="compact" mark="bullet">
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<listitem>
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<para>
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Running the <productname>PostgreSQL</productname> interactive
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terminal program, called <application><firstterm>psql</firstterm></application>, which allows you
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to interactively enter, edit, and execute
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<acronym>SQL</acronym> commands.
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</para>
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</listitem>
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<listitem>
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<para>
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Using an existing graphical frontend tool like
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<application>pgAdmin</application> or an office suite with
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<acronym>ODBC</acronym> or <acronym>JDBC</acronym> support to create and manipulate a
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database. These possibilities are not covered in this
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tutorial.
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</para>
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</listitem>
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<listitem>
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<para>
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Writing a custom application, using one of the several
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available language bindings. These possibilities are discussed
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further in <xref linkend="client-interfaces"/>.
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</para>
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</listitem>
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</itemizedlist>
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You probably want to start up <command>psql</command> to try
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the examples in this tutorial. It can be activated for the
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<literal>mydb</literal> database by typing the command:
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<screen>
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<prompt>$</prompt> <userinput>psql mydb</userinput>
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</screen>
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If you do not supply the database name then it will default to your
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user account name. You already discovered this scheme in the
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previous section using <command>createdb</command>.
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</para>
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<para>
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In <command>psql</command>, you will be greeted with the following
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message:
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<screen>
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psql (&version;)
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Type "help" for help.
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mydb=>
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</screen>
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<indexterm><primary>superuser</primary></indexterm>
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The last line could also be:
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<screen>
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mydb=#
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</screen>
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That would mean you are a database superuser, which is most likely
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the case if you installed the <productname>PostgreSQL</productname> instance
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yourself. Being a superuser means that you are not subject to
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access controls. For the purposes of this tutorial that is not
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important.
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</para>
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<para>
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If you encounter problems starting <command>psql</command>
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then go back to the previous section. The diagnostics of
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<command>createdb</command> and <command>psql</command> are
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similar, and if the former worked the latter should work as well.
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</para>
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<para>
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The last line printed out by <command>psql</command> is the
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prompt, and it indicates that <command>psql</command> is listening
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to you and that you can type <acronym>SQL</acronym> queries into a
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work space maintained by <command>psql</command>. Try out these
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commands:
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<indexterm><primary>version</primary></indexterm>
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<screen>
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<prompt>mydb=></prompt> <userinput>SELECT version();</userinput>
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version
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-------------------------------------------------------------------&zwsp;-----------------------
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PostgreSQL &version; on x86_64-pc-linux-gnu, compiled by gcc (Debian 4.9.2-10) 4.9.2, 64-bit
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(1 row)
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<prompt>mydb=></prompt> <userinput>SELECT current_date;</userinput>
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date
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------------
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2016-01-07
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(1 row)
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<prompt>mydb=></prompt> <userinput>SELECT 2 + 2;</userinput>
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?column?
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----------
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4
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(1 row)
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</screen>
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</para>
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<para>
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The <command>psql</command> program has a number of internal
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commands that are not SQL commands. They begin with the backslash
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character, <quote><literal>\</literal></quote>.
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For example,
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you can get help on the syntax of various
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<productname>PostgreSQL</productname> <acronym>SQL</acronym>
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commands by typing:
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<screen>
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<prompt>mydb=></prompt> <userinput>\h</userinput>
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</screen>
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</para>
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<para>
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To get out of <command>psql</command>, type:
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<screen>
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<prompt>mydb=></prompt> <userinput>\q</userinput>
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</screen>
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and <command>psql</command> will quit and return you to your
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command shell. (For more internal commands, type
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<literal>\?</literal> at the <command>psql</command> prompt.) The
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full capabilities of <command>psql</command> are documented in
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<xref linkend="app-psql"/>. In this tutorial we will not use these
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features explicitly, but you can use them yourself when it is helpful.
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</para>
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</sect1>
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</chapter>
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