doc/src/sgml/start.sgml

   1 <!-- $PostgreSQL$ -->
   2
   3  <chapter id="tutorial-start">
   4   <title>Getting Started</title>
   5
   6   <sect1 id="tutorial-install">
   7    <title>Installation</title>
   8
   9    <para>
  10     Before you can use <productname>PostgreSQL</productname> you need
  11     to install it, of course.  It is possible that
  12     <productname>PostgreSQL</productname> is already installed at your
  13     site, either because it was included in your operating system
  14     distribution or because the system administrator already installed
  15     it.  If that is the case, you should obtain information from the
  16     operating system documentation or your system administrator about
  17     how to access <productname>PostgreSQL</productname>.
  18    </para>
  19
  20    <para>
  21     If you are not sure whether <productname>PostgreSQL</productname>
  22     is already available or whether you can use it for your
  23     experimentation then you can install it yourself.  Doing so is not
  24     hard and it can be a good exercise.
  25     <productname>PostgreSQL</productname> can be installed by any
  26     unprivileged user; no superuser (<systemitem>root</systemitem>)
  27     access is required.
  28    </para>
  29
  30    <para>
  31     If you are installing <productname>PostgreSQL</productname>
  32     yourself, then refer to <xref linkend="installation">
  33     for instructions on installation, and return to
  34     this guide when the installation is complete.  Be sure to follow
  35     closely the section about setting up the appropriate environment
  36     variables.
  37    </para>
  38
  39    <para>
  40     If your site administrator has not set things up in the default
  41     way, you might have some more work to do.  For example, if the
  42     database server machine is a remote machine, you will need to set
  43     the <envar>PGHOST</envar> environment variable to the name of the
  44     database server machine.  The environment variable
  45     <envar>PGPORT</envar> might also have to be set.  The bottom line is
  46     this: if you try to start an application program and it complains
  47     that it cannot connect to the database, you should consult your
  48     site administrator or, if that is you, the documentation to make
  49     sure that your environment is properly set up.  If you did not
  50     understand the preceding paragraph then read the next section.
  51    </para>
  52   </sect1>
  53
  54
  55   <sect1 id="tutorial-arch">
  56    <title>Architectural Fundamentals</title>
  57
  58    <para>
  59     Before we proceed, you should understand the basic
  60     <productname>PostgreSQL</productname> system architecture.
  61     Understanding how the parts of
  62     <productname>PostgreSQL</productname> interact will make this
  63     chapter somewhat clearer.
  64    </para>
  65
  66    <para>
  67     In database jargon, <productname>PostgreSQL</productname> uses a
  68     client/server model.  A <productname>PostgreSQL</productname>
  69     session consists of the following cooperating processes
  70     (programs):
  71
  72     <itemizedlist>
  73      <listitem>
  74       <para>
  75        A server process, which manages the database files, accepts
  76        connections to the database from client applications, and
  77        performs actions on the database on behalf of the clients.  The
  78        database server program is called
  79        <filename>postgres</filename>.
  80        <indexterm><primary>postgres</primary></indexterm>
  81       </para>
  82      </listitem>
  83
  84      <listitem>
  85       <para>
  86        The user's client (frontend) application that wants to perform
  87        database operations.  Client applications can be very diverse
  88        in nature:  a client could be a text-oriented tool, a graphical
  89        application, a web server that accesses the database to
  90        display web pages, or a specialized database maintenance tool.
  91        Some client applications are supplied with the
  92        <productname>PostgreSQL</productname> distribution; most are
  93        developed by users.
  94       </para>
  95      </listitem>
  96
  97     </itemizedlist>
  98    </para>
  99
 100    <para>
 101     As is typical of client/server applications, the client and the
 102     server can be on different hosts.  In that case they communicate
 103     over a TCP/IP network connection.  You should keep this in mind,
 104     because the files that can be accessed on a client machine might
 105     not be accessible (or might only be accessible using a different
 106     file name) on the database server machine.
 107    </para>
 108
 109    <para>
 110     The <productname>PostgreSQL</productname> server can handle
 111     multiple concurrent connections from clients.  For that purpose it
 112     starts (<quote>forks</quote>) a new process for each connection.
 113     From that point on, the client and the new server process
 114     communicate without intervention by the original
 115     <filename>postgres</filename> process.  Thus, the
 116     master server process is always running, waiting for
 117     client connections, whereas client and associated server processes
 118     come and go.  (All of this is of course invisible to the user.  We
 119     only mention it here for completeness.)
 120    </para>
 121   </sect1>
 122
 123
 124   <sect1 id="tutorial-createdb">
 125    <title>Creating a Database</title>
 126
 127    <indexterm zone="tutorial-createdb">
 128     <primary>database</primary>
 129     <secondary>creating</secondary>
 130    </indexterm>
 131
 132    <indexterm zone="tutorial-createdb">
 133     <primary>createdb</primary>
 134    </indexterm>
 135
 136    <para>
 137     The first test to see whether you can access the database server
 138     is to try to create a database.  A running
 139     <productname>PostgreSQL</productname> server can manage many
 140     databases.  Typically, a separate database is used for each
 141     project or for each user.
 142    </para>
 143
 144    <para>
 145     Possibly, your site administrator has already created a database
 146     for your use.  He should have told you what the name of your
 147     database is.  In that case you can omit this step and skip ahead
 148     to the next section.
 149    </para>
 150
 151    <para>
 152     To create a new database, in this example named
 153     <literal>mydb</literal>, you use the following command:
 154 <screen>
 155 <prompt>$</prompt> <userinput>createdb mydb</userinput>
 156 </screen>
 157     If this produces no response then this step was successful and you can skip over the
 158     remainder of this section.
 159    </para>
 160
 161    <para>
 162     If you see a message similar to
 163 <screen>
 164 createdb: command not found
 165 </screen>
 166     then <productname>PostgreSQL</> was not installed properly.  Either it was not
 167     installed at all or the search path was not set correctly.  Try
 168     calling the command with an absolute path instead:
 169 <screen>
 170 <prompt>$</prompt> <userinput>/usr/local/pgsql/bin/createdb mydb</userinput>
 171 </screen>
 172     The path at your site might be different.  Contact your site
 173     administrator or check back in the installation instructions to
 174     correct the situation.
 175    </para>
 176
 177    <para>
 178     Another response could be this:
 179 <screen>
 180 createdb: could not connect to database postgres: could not connect to server: No such file or directory
 181         Is the server running locally and accepting
 182         connections on Unix domain socket "/tmp/.s.PGSQL.5432"?
 183 </screen>
 184     This means that the server was not started, or it was not started
 185     where <command>createdb</command> expected it.  Again, check the
 186     installation instructions or consult the administrator.
 187    </para>
 188
 189    <para>
 190     Another response could be this:
 191 <screen>
 192 createdb: could not connect to database postgres: FATAL:  role "joe" does not exist
 193 </screen>
 194     where your own login name is mentioned.  This will happen if the
 195     administrator has not created a <productname>PostgreSQL</> user account
 196     for you.  (<productname>PostgreSQL</> user accounts are distinct from
 197     operating system user accounts.)  If you are the administrator, see
 198     <xref linkend="user-manag"> for help creating accounts.  You will need to
 199     become the operating system user under which <productname>PostgreSQL</>
 200     was installed (usually <literal>postgres</>) to create the first user
 201     account.  It could also be that you were assigned a
 202     <productname>PostgreSQL</> user name that is different from your
 203     operating system user name; in that case you need to use the <option>-U</>
 204     switch or set the <envar>PGUSER</> environment variable to specify your
 205     <productname>PostgreSQL</> user name.
 206    </para>
 207
 208    <para>
 209     If you have a user account but it does not have the privileges required to
 210     create a database, you will see the following:
 211 <screen>
 212 createdb: database creation failed: ERROR:  permission denied to create database
 213 </screen>
 214     Not every user has authorization to create new databases.  If
 215     <productname>PostgreSQL</productname> refuses to create databases
 216     for you then the site administrator needs to grant you permission
 217     to create databases.  Consult your site administrator if this
 218     occurs.  If you installed <productname>PostgreSQL</productname>
 219     yourself then you should log in for the purposes of this tutorial
 220     under the user account that you started the server as.
 221
 222     <footnote>
 223      <para>
 224       As an explanation for why this works:
 225       <productname>PostgreSQL</productname> user names are separate
 226       from operating system user accounts.  When you connect to a
 227       database, you can choose what
 228       <productname>PostgreSQL</productname> user name to connect as;
 229       if you don't, it will default to the same name as your current
 230       operating system account.  As it happens, there will always be a
 231       <productname>PostgreSQL</productname> user account that has the
 232       same name as the operating system user that started the server,
 233       and it also happens that that user always has permission to
 234       create databases.  Instead of logging in as that user you can
 235       also specify the <option>-U</option> option everywhere to select
 236       a <productname>PostgreSQL</productname> user name to connect as.
 237      </para>
 238     </footnote>
 239    </para>
 240
 241    <para>
 242     You can also create databases with other names.
 243     <productname>PostgreSQL</productname> allows you to create any
 244     number of databases at a given site.  Database names must have an
 245     alphabetic first character and are limited to 63 characters in
 246     length.  A convenient choice is to create a database with the same
 247     name as your current user name.  Many tools assume that database
 248     name as the default, so it can save you some typing.  To create
 249     that database, simply type
 250 <screen>
 251 <prompt>$</prompt> <userinput>createdb</userinput>
 252 </screen>
 253    </para>
 254
 255    <para>
 256     If you do not want to use your database anymore you can remove it.
 257     For example, if you are the owner (creator) of the database
 258     <literal>mydb</literal>, you can destroy it using the following
 259     command:
 260 <screen>
 261 <prompt>$</prompt> <userinput>dropdb mydb</userinput>
 262 </screen>
 263     (For this command, the database name does not default to the user
 264     account name.  You always need to specify it.)  This action
 265     physically removes all files associated with the database and
 266     cannot be undone, so this should only be done with a great deal of
 267     forethought.
 268    </para>
 269
 270    <para>
 271     More about <command>createdb</command> and <command>dropdb</command> can
 272     be found in <xref linkend="APP-CREATEDB"> and <xref linkend="APP-DROPDB">
 273     respectively.
 274    </para>
 275   </sect1>
 276
 277
 278   <sect1 id="tutorial-accessdb">
 279    <title>Accessing a Database</title>
 280
 281    <indexterm zone="tutorial-accessdb">
 282     <primary>psql</primary>
 283    </indexterm>
 284
 285    <para>
 286     Once you have created a database, you can access it by:
 287
 288     <itemizedlist spacing="compact" mark="bullet">
 289      <listitem>
 290       <para>
 291        Running the <productname>PostgreSQL</productname> interactive
 292        terminal program, called <application><firstterm>psql</></application>, which allows you
 293        to interactively enter, edit, and execute
 294        <acronym>SQL</acronym> commands.
 295       </para>
 296      </listitem>
 297
 298      <listitem>
 299       <para>
 300        Using an existing graphical frontend tool like
 301        <application>pgAdmin</application> or an office suite with
 302        <acronym>ODBC</acronym> support to create and manipulate a
 303        database.  These possibilities are not covered in this
 304        tutorial.
 305       </para>
 306      </listitem>
 307
 308      <listitem>
 309       <para>
 310        Writing a custom application, using one of the several
 311        available language bindings.  These possibilities are discussed
 312        further in <xref linkend="client-interfaces">.
 313       </para>
 314      </listitem>
 315     </itemizedlist>
 316
 317     You probably want to start up <command>psql</command>, to try out
 318     the examples in this tutorial.  It can be activated for the
 319     <literal>mydb</literal> database by typing the command:
 320 <screen>
 321 <prompt>$</prompt> <userinput>psql mydb</userinput>
 322 </screen>
 323     If you leave off the database name then it will default to your
 324     user account name.  You already discovered this scheme in the
 325     previous section.
 326    </para>
 327
 328    <para>
 329     In <command>psql</command>, you will be greeted with the following
 330     message:
 331 <screen>
 332 psql (&version;)
 333 Type "help" for help.
 334
 335 mydb=&gt;
 336 </screen>
 337     <indexterm><primary>superuser</primary></indexterm>
 338     The last line could also be
 339 <screen>
 340 mydb=#
 341 </screen>
 342     That would mean you are a database superuser, which is most likely
 343     the case if you installed <productname>PostgreSQL</productname>
 344     yourself.  Being a superuser means that you are not subject to
 345     access controls.  For the purposes of this tutorial that is not of
 346     importance.
 347    </para>
 348
 349    <para>
 350     If you encounter problems starting <command>psql</command>
 351     then go back to the previous section.  The diagnostics of
 352     <command>createdb</command> and <command>psql</command> are
 353     similar, and if the former worked the latter should work as well.
 354    </para>
 355
 356    <para>
 357     The last line printed out by <command>psql</command> is the
 358     prompt, and it indicates that <command>psql</command> is listening
 359     to you and that you can type <acronym>SQL</acronym> queries into a
 360     work space maintained by <command>psql</command>.  Try out these
 361     commands:
 362     <indexterm><primary>version</primary></indexterm>
 363 <screen>
 364 <prompt>mydb=&gt;</prompt> <userinput>SELECT version();</userinput>
 365                                version
 366  -----------------------------------------------------------------------
 367  PostgreSQL &version; on i586-pc-linux-gnu, compiled by GCC 2.96, 32-bit
 368 (1 row)
 369
 370 <prompt>mydb=&gt;</prompt> <userinput>SELECT current_date;</userinput>
 371     date
 372 ------------
 373  2002-08-31
 374 (1 row)
 375
 376 <prompt>mydb=&gt;</prompt> <userinput>SELECT 2 + 2;</userinput>
 377  ?column?
 378 ----------
 379         4
 380 (1 row)
 381 </screen>
 382    </para>
 383
 384    <para>
 385     The <command>psql</command> program has a number of internal
 386     commands that are not SQL commands.  They begin with the backslash
 387     character, <quote><literal>\</literal></quote>.  Some of these
 388     commands were listed in the welcome message.  For example,
 389     you can get help on the syntax of various
 390     <productname>PostgreSQL</productname> <acronym>SQL</acronym>
 391     commands by typing:
 392 <screen>
 393 <prompt>mydb=&gt;</prompt> <userinput>\h</userinput>
 394 </screen>
 395    </para>
 396
 397    <para>
 398     To get out of <command>psql</command>, type
 399 <screen>
 400 <prompt>mydb=&gt;</prompt> <userinput>\q</userinput>
 401 </screen>
 402     and <command>psql</command> will quit and return you to your
 403     command shell. (For more internal commands, type
 404     <literal>\?</literal> at the <command>psql</command> prompt.)  The
 405     full capabilities of <command>psql</command> are documented in
 406     <xref linkend="app-psql">.  If <productname>PostgreSQL</> is
 407     installed correctly you can also type <literal>man psql</literal>
 408     at the operating system shell prompt to see the documentation.  In
 409     this tutorial we will not use these features explicitly, but you
 410     can use them yourself when you see fit.
 411    </para>
 412
 413   </sect1>
 414  </chapter>