Add a materialized view relations.

A materialized view has a rule just like a view and a heap and
other physical properties like a table.  The rule is only used to
populate the table, references in queries refer to the
materialized data.

This is a minimal implementation, but should still be useful in
many cases.  Currently data is only populated "on demand" by the
CREATE MATERIALIZED VIEW and REFRESH MATERIALIZED VIEW statements.
It is expected that future releases will add incremental updates
with various timings, and that a more refined concept of defining
what is "fresh" data will be developed.  At some point it may even
be possible to have queries use a materialized in place of
references to underlying tables, but that requires the other
above-mentioned features to be working first.

Much of the documentation work by Robert Haas.
Review by Noah Misch, Thom Brown, Robert Haas, Marko Tiikkaja
Security review by KaiGai Kohei, with a decision on how best to
implement sepgsql still pending.

doc/src/sgml/ref/create_materialized_view.sgml

@@ -0,0 +1,154 @@
+<!--
+doc/src/sgml/ref/create_materialized_view.sgml
+PostgreSQL documentation
+-->
+
+<refentry id="SQL-CREATEMATERIALIZEDVIEW">
+ <refmeta>
+  <refentrytitle>CREATE MATERIALIZED VIEW</refentrytitle>
+  <manvolnum>7</manvolnum>
+  <refmiscinfo>SQL - Language Statements</refmiscinfo>
+ </refmeta>
+
+ <refnamediv>
+  <refname>CREATE MATERIALIZED VIEW</refname>
+  <refpurpose>define a new materialized view</refpurpose>
+ </refnamediv>
+
+ <indexterm zone="sql-creatematerializedview">
+  <primary>CREATE MATERIALIZED VIEW</primary>
+ </indexterm>
+
+ <refsynopsisdiv>
+<synopsis>
+CREATE [ UNLOGGED ] MATERIALIZED VIEW <replaceable>table_name</replaceable>
+    [ (<replaceable>column_name</replaceable> [, ...] ) ]
+    [ WITH ( <replaceable class="PARAMETER">storage_parameter</replaceable> [= <replaceable class="PARAMETER">value</replaceable>] [, ... ] ) ]
+    [ TABLESPACE <replaceable class="PARAMETER">tablespace_name</replaceable> ]
+    AS <replaceable>query</replaceable>
+    [ WITH [ NO ] DATA ]
+</synopsis>
+ </refsynopsisdiv>
+
+ <refsect1>
+  <title>Description</title>
+
+  <para>
+   <command>CREATE MATERIALIZED VIEW</command> defines a materialized view of
+   a query.  The query is executed and used to populate the view at the time
+   the command is issued (unless <command>WITH NO DATA</> is used) and may be
+   refreshed later using <command>REFRESH MATERIALIZED VIEW</command>.
+  </para>
+
+  <para>
+   <command>CREATE MATERIALIZED VIEW</command> is similar to
+   <command>CREATE TABLE AS</>, except that it also remembers the query used
+   to initialize the view, so that it can be refreshed later upon demand.
+  </para>
+ </refsect1>
+
+ <refsect1>
+  <title>Parameters</title>
+
+  <variablelist>
+   <varlistentry>
+    <term><literal>UNLOGGED</></term>
+    <listitem>
+     <para>
+      If specified, the materialized view will be unlogged.
+      Refer to <xref linkend="sql-createtable"> for details.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable>table_name</replaceable></term>
+    <listitem>
+     <para>
+      The name (optionally schema-qualified) of the materialized view to be
+      created.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable>column_name</replaceable></term>
+    <listitem>
+     <para>
+      The name of a column in the new materialized view.  If column names are
+      not provided, they are taken from the output column names of the query.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><literal>WITH ( <replaceable class="PARAMETER">storage_parameter</replaceable> [= <replaceable class="PARAMETER">value</replaceable>] [, ... ] )</literal></term>
+    <listitem>
+     <para>
+      This clause specifies optional storage parameters for the new
+      materialized view; see <xref linkend="sql-createtable-storage-parameters"
+      endterm="sql-createtable-storage-parameters-title"> for more
+      information.
+      See <xref linkend="sql-createtable"> for more information.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><literal>TABLESPACE <replaceable class="PARAMETER">tablespace_name</replaceable></literal></term>
+    <listitem>
+     <para>
+      The <replaceable class="PARAMETER">tablespace_name</replaceable> is the name
+      of the tablespace in which the new materialized view is to be created.
+      If not specified, <xref linkend="guc-default-tablespace"> is consulted.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable>query</replaceable></term>
+    <listitem>
+     <para>
+      A <xref linkend="sql-select">, <link linkend="sql-table">TABLE</link>,
+      or <xref linkend="sql-values"> command.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><literal>WITH [ NO ] DATA</></term>
+    <listitem>
+     <para>
+      This clause specifies whether or not the materialized view should be
+      populated at creation time.  If not, the materialized view will be
+      flagged as unscannable and cannot be queried until <command>REFRESH
+      MATERIALIZED VIEW</> is used.
+     </para>
+    </listitem>
+   </varlistentry>
+
+  </variablelist>
+ </refsect1>
+
+ <refsect1>
+  <title>Compatibility</title>
+
+  <para>
+   <command>CREATE MATERIALIZED VIEW</command> is a
+   <productname>PostgreSQL</productname> extension.
+  </para>
+ </refsect1>
+
+ <refsect1>
+  <title>See Also</title>
+
+  <simplelist type="inline">
+   <member><xref linkend="sql-altermaterializedview"></member>
+   <member><xref linkend="sql-createtableas"></member>
+   <member><xref linkend="sql-createview"></member>
+   <member><xref linkend="sql-dropmaterializedview"></member>
+   <member><xref linkend="sql-refreshmaterializedview"></member>
+  </simplelist>
+ </refsect1>
+
+</refentry>