ways of
    organizing databases.  Files and directories on Unix-like
    operating systems form an example of a hierarchical database.  A
    more modern development is the object-oriented database.
   </para>

   <para>
    <indexterm><primary>row</primary></indexterm>
    <indexterm><primary>column</primary></indexterm>

    Each table is a named collection of <firstterm>rows</firstterm>.
    Each row of a given table has the same set of named
    <firstterm>columns</firstterm>,
    and each column is of a specific data type.  Whereas columns have
    a fixed order in each row, it is important to remember that SQL
    does not guarantee the order of the rows within the table in any
    way (although they can be explicitly sorted for display).
   </para>

   <para>
    <indexterm><primary>database cluster</primary></indexterm>
    <indexterm><primary>cluster</primary><secondary>of databases</secondary><see>database cluster</see></indexterm>

    Tables are grouped into databases, and a collection of databases
    managed by a single <productname>PostgreSQL</productname> server
    instance constitutes a database <firstterm>cluster</firstterm>.
   </para>
  </sect1>


  <sect1 id="tutorial-table">
   <title>Creating a New Table</title>

   <indexterm zone="tutorial-table">
    <primary>CREATE TABLE</primary>
   </indexterm>

   <para>
    You  can  create  a  new  table by specifying the table
    name, along with all column names and their types:

<programlisting>
CREATE TABLE weather (
    city            varchar(80),
    temp_lo         int,           -- low temperature
    temp_hi         int,           -- high temperature
    prcp            real,          -- precipitation
    date            date
);
</programlisting>

    You can enter this into <command>psql</command> with the line
    breaks.  <command>psql</command> will recognize that the command
    is not terminated until the semicolon.
   </para>

   <para>
    White space (i.e., spaces, tabs, and newlines) can be used freely
    in SQL commands.  That means you can type the command aligned
    differently than above, or even all on one line.  Two dashes
    (<quote><literal>--</literal></quote>) introduce comments.
    Whatever follows them is ignored up to the end of the line.  SQL
    is case-insensitive about key words and identifiers, except
    when identifiers are double-quoted to preserve the case (not done
    above).
   </para>

   <para>
    <type>varchar(80)</type> specifies a data type that can store
    arbitrary character strings up to 80 characters in length.
    <type>int</type> is the normal integer type.  <type>real</type> is
    a type for storing single precision floating-point numbers.
    <type>date</type> should be self-explanatory.  (Yes, the column of
    type <type>date</type> is also named <structfield>date</structfield>.
    This might be convenient or confusing &mdash; you choose.)
   </para>

   <para>
    <productname>PostgreSQL</productname> supports the standard
    <acronym>SQL</acronym> types <type>int</type>,
    <type>smallint</type>, <type>real</type>, <type>double
    precision</type>, <type>char(<replaceable>N</replaceable>)</type>,
    <type>varchar(<replaceable>N</replaceable>)</type>, <type>date</type>,
    <type>time</type>, <type>timestamp</type>, and
    <type>interval</type>, as well as other types of general utility
    and a rich set of geometric types.
    <productname>PostgreSQL</productname> can be customized with an
    arbitrary number of user-defined data types.  Consequently, type
    names are not key words in the syntax, except where required to
    support special cases in the <acronym>SQL</acronym> standard.
   </para>

   <para>
    The second example will store cities and their associated
    geographical location:
<programlisting>
CREATE TABLE cities (
    name            varchar(80),
    location        point
);
</programlisting>
    The <type>point</type> type is an example of a
    <productname>PostgreSQL</productname>-specific