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$PostgreSQL: pgsql/doc/src/sgml/ref/create_table_as.sgml,v 1.32 2006/02/19 00:04:26 neilc Exp $
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<refentry id="SQL-CREATETABLEAS">
 <refmeta>
  <refentrytitle id="sql-createtableas-title">CREATE TABLE AS</refentrytitle>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>

 <refnamediv>
  <refname>CREATE TABLE AS</refname>
  <refpurpose>define a new table from the results of a query</refpurpose>
 </refnamediv>

 <indexterm zone="sql-createtableas">
  <primary>CREATE TABLE AS</primary>
 </indexterm>

 <refsynopsisdiv>
<synopsis>
CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } ] TABLE <replaceable>table_name</replaceable>
    [ (<replaceable>column_name</replaceable> [, ...] ) ]
    [ WITH OIDS | WITHOUT OIDS ]
    [ ON COMMIT { PRESERVE ROWS | DELETE ROWS | DROP } ]
    [ TABLESPACE <replaceable class="PARAMETER">tablespace</replaceable> ]
    AS <replaceable>query</replaceable>
</synopsis>
 </refsynopsisdiv>
  
 <refsect1>
  <title>Description</title>

  <para>
   <command>CREATE TABLE AS</command> creates a table and fills it
   with data computed by a <command>SELECT</command> command or an
   <command>EXECUTE</command> that runs a prepared
   <command>SELECT</command> command.  The table columns have the
   names and data types associated with the output columns of the
   <command>SELECT</command> (except that you can override the column
   names by giving an explicit list of new column names).
  </para>

  <para>
   <command>CREATE TABLE AS</command> bears some resemblance to
   creating a view, but it is really quite different: it creates a new
   table and evaluates the query just once to fill the new table
   initially.  The new table will not track subsequent changes to the
   source tables of the query.  In contrast, a view re-evaluates its
   defining <command>SELECT</command> statement whenever it is
   queried.
  </para>
 </refsect1>

 <refsect1>
  <title>Parameters</title>

  <variablelist>
   <varlistentry>
    <term><literal>GLOBAL</literal> or <literal>LOCAL</literal></term>
    <listitem>
     <para>
      Ignored for compatibility. Refer to <xref
      linkend="sql-createtable" endterm="sql-createtable-title"> for
      details.
     </para>
    </listitem>
   </varlistentry>
  </variablelist>

  <variablelist>
   <varlistentry>
    <term><literal>TEMPORARY</> or <literal>TEMP</></term>
    <listitem>
     <para>
      If specified, the table is created as a temporary table.
      Refer to <xref linkend="sql-createtable" endterm="sql-createtable-title"> for details.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable>table_name</replaceable></term>
    <listitem>
     <para>
      The name (optionally schema-qualified) of the table to be created.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable>column_name</replaceable></term>
    <listitem>
     <para>
      The name of a column in the new table.  If column names are not
      provided, they are taken from the output column names of the
      query.  If the table is created from an
      <command>EXECUTE</command> command, a column name list cannot be
      specified.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>WITH OIDS</literal></term>
    <term><literal>WITHOUT OIDS</literal></term>
     <listitem>
      <para>
       This optional clause specifies whether the table created by
       <command>CREATE TABLE AS</command> should include OIDs. If
       neither form of this clause is specified, the value of the
       <xref linkend="guc-default-with-oids"> configuration parameter is
       used.
      </para>
     </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>ON COMMIT</literal></term>
    <listitem>
     <para>
      The behavior of temporary tables at the end of a transaction
      block can be controlled using <literal>ON COMMIT</literal>.
      The three options are:

      <variablelist>
       <varlistentry>
        <term><literal>PRESERVE ROWS</literal></term>
        <listitem>
         <para>
          No special action is taken at the ends of transactions.
          This is the default behavior.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry>
        <term><literal>DELETE ROWS</literal></term>
        <listitem>
         <para>
          All rows in the temporary table will be deleted at the end
          of each transaction block.  Essentially, an automatic <xref
          linkend="sql-truncate" endterm="sql-truncate-title"> is done
          at each commit.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry>
        <term><literal>DROP</literal></term>
        <listitem>
         <para>
          The temporary table will be dropped at the end of the current
          transaction block.
         </para>
        </listitem>
       </varlistentry>
      </variablelist>
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>TABLESPACE <replaceable class="PARAMETER">tablespace</replaceable></literal></term>
    <listitem>
     <para>
      The <replaceable class="PARAMETER">tablespace</replaceable> is the name
      of the tablespace in which the new table is to be created.
      If not specified,
      <xref linkend="guc-default-tablespace"> is used, or the database's
      default tablespace if <varname>default_tablespace</> is an empty
      string.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable>query</replaceable></term>
    <listitem>
     <para>
      A query statement (that is, a <command>SELECT</command> command
      or an <command>EXECUTE</command> command that runs a prepared
      <command>SELECT</command> command).  Refer to <xref
      linkend="sql-select" endterm="sql-select-title"> or <xref
      linkend="sql-execute" endterm="sql-execute-title">,
      respectively, for a description of the allowed syntax.
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Notes</title>

  <para>
   This command is functionally similar to <xref
   linkend="sql-selectinto" endterm="sql-selectinto-title">, but it is
   preferred since it is less likely to be confused with other uses of
   the <command>SELECT INTO</> syntax. Furthermore, <command>CREATE
   TABLE AS</command> offers a superset of the functionality offered
   by <command>SELECT INTO</command>.
  </para>

  <para>
   Prior to <productname>PostgreSQL</productname> 8.0, <command>CREATE
   TABLE AS</command> always included OIDs in the table it
   created.  As of <productname>PostgreSQL</productname> 8.0,
   the <command>CREATE TABLE AS</command> command allows the user to
   explicitly specify whether OIDs should be included. If the
   presence of OIDs is not explicitly specified,
   the <xref linkend="guc-default-with-oids"> configuration variable is
   used.  As of <productname>PostgreSQL</productname> 8.1,
   this variable is false by default, so the default behavior is not
   identical to pre-8.0 releases.  Applications that
   require OIDs in the table created by <command>CREATE TABLE
   AS</command> should explicitly specify <literal>WITH OIDS</literal>
   to ensure proper behavior.
  </para>
 </refsect1>

 <refsect1>
  <title>Examples</title>

  <para>
   Create a new table <literal>films_recent</literal> consisting of only
   recent entries from the table <literal>films</literal>:

<programlisting>
CREATE TABLE films_recent AS
  SELECT * FROM films WHERE date_prod &gt;= '2002-01-01';
</programlisting>
  </para>

  <para>
   Create a new temporary table that will be dropped at commit
   <literal>films_recent</literal> with oids consisting of only
   recent entries from the table <literal>films</literal> using a
   prepared statement:

<programlisting>
PREPARE recentfilms(date) AS
  SELECT * FROM films WHERE date_prod &gt; $1;
CREATE TEMP TABLE films_recent WITH OIDS ON COMMIT DROP AS
  EXECUTE recentfilms('2002-01-01');
</programlisting>
  </para>
 </refsect1>

 <refsect1>
  <title>Compatibility</title>

  <para>
   <command>CREATE TABLE AS</command> conforms to the <acronym>SQL</acronym>
   standard, with the following exceptions:

   <itemizedlist spacing="compact">
    <listitem>
     <para>
      The standard requires parentheses around the subquery clause; in
      <productname>PostgreSQL</productname>, these parentheses are
      optional.
     </para>
    </listitem>

    <listitem>
     <para>
      The standard defines a <literal>WITH [ NO ] DATA</literal> clause;
      this is not currently implemented by <productname>PostgreSQL</>.
      The behavior provided by <productname>PostgreSQL</> is equivalent
      to the standard's <literal>WITH DATA</literal> case.
     </para>
    </listitem>

    <listitem>
     <para>
      <literal>WITH/WITHOUT OIDS</> is a <productname>PostgreSQL</>
      extension.
     </para>
    </listitem>

    <listitem>
     <para>
      <productname>PostgreSQL</> handles temporary tables in a way
      rather different from the standard; see
      <xref linkend="sql-createtable" endterm="sql-createtable-title">
      for details.
     </para>
    </listitem>

    <listitem>
     <para>
      The <productname>PostgreSQL</productname> concept of tablespaces is not
      part of the standard.  Hence, the clause <literal>TABLESPACE</literal>
      is an extension.
     </para>
    </listitem>
   </itemizedlist>
  </para>
 </refsect1>

 <refsect1>
  <title>See Also</title>

  <simplelist type="inline">
   <member><xref linkend="sql-createtable" endterm="sql-createtable-title"></member>
   <member><xref linkend="sql-execute" endterm="sql-execute-title"></member>
   <member><xref linkend="sql-select" endterm="sql-select-title"></member>
   <member><xref linkend="sql-selectinto" endterm="sql-selectinto-title"></member>
  </simplelist>
 </refsect1>
 
</refentry>

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