doc/src/sgml/ref/create_view.sgml - cloudberry - Git at Google

 <!--
 doc/src/sgml/ref/create_view.sgml
 PostgreSQL documentation
 -->

 <refentry id="sql-createview">
  <indexterm zone="sql-createview">
   <primary>CREATE VIEW</primary>
  </indexterm>

  <refmeta>
   <refentrytitle>CREATE VIEW</refentrytitle>
   <manvolnum>7</manvolnum>
   <refmiscinfo>SQL - Language Statements</refmiscinfo>
  </refmeta>

  <refnamediv>
   <refname>CREATE VIEW</refname>
   <refpurpose>define a new view</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
 <synopsis>
 CREATE [ OR REPLACE ] [ TEMP | TEMPORARY ] [ RECURSIVE ] VIEW <replaceable class="parameter">name</replaceable> [ ( <replaceable class="parameter">column_name</replaceable> [, ...] ) ]
     [ WITH ( <replaceable class="parameter">view_option_name</replaceable> [= <replaceable class="parameter">view_option_value</replaceable>] [, ... ] ) ]
     AS <replaceable class="parameter">query</replaceable>
     [ WITH [ CASCADED | LOCAL ] CHECK OPTION ]
 </synopsis>
  </refsynopsisdiv>

  <refsect1>
   <title>Description</title>

   <para>
    <command>CREATE VIEW</command> defines a view of a query.  The view
    is not physically materialized. Instead, the query is run every time
    the view is referenced in a query.
   </para>

   <para>
    <command>CREATE OR REPLACE VIEW</command> is similar, but if a view
    of the same name already exists, it is replaced.  The new query must
    generate the same columns that were generated by the existing view query
    (that is, the same column names in the same order and with the same data
    types), but it may add additional columns to the end of the list.  The
    calculations giving rise to the output columns may be completely different.
   </para>

   <para>
    If a schema name is given (for example, <literal>CREATE VIEW
    myschema.myview ...</literal>) then the view is created in the specified
    schema.  Otherwise it is created in the current schema.  Temporary
    views exist in a special schema, so a schema name cannot be given
    when creating a temporary view. The name of the view must be
    distinct from the name of any other view, table, sequence, index or foreign table
    in the same schema.
   </para>
  </refsect1>

  <refsect1>
   <title>Parameters</title>

   <variablelist>
    <varlistentry>
     <term><literal>TEMPORARY</literal> or <literal>TEMP</literal></term>
     <listitem>
      <para>
       If specified, the view is created as a temporary view.
       Temporary views are automatically dropped at the end of the
       current session.  Existing
       permanent relations with the same name are not visible to the
       current session while the temporary view exists, unless they are
       referenced with schema-qualified names.
      </para>

      <para>
       If any of the tables referenced by the view are temporary,
       the view is created as a temporary view (whether
       <literal>TEMPORARY</literal> is specified or not).
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><literal>RECURSIVE</literal>
       <indexterm zone="sql-createview">
        <primary>RECURSIVE</primary>
        <secondary>in views</secondary>
       </indexterm>
     </term>
     <listitem>
      <para>
       Creates a recursive view.  The syntax
 <synopsis>
 CREATE RECURSIVE VIEW [ <replaceable>schema</replaceable> . ] <replaceable>view_name</replaceable> (<replaceable>column_names</replaceable>) AS SELECT <replaceable>...</replaceable>;
 </synopsis>
       is equivalent to
 <synopsis>
 CREATE VIEW [ <replaceable>schema</replaceable> . ] <replaceable>view_name</replaceable> AS WITH RECURSIVE <replaceable>view_name</replaceable> (<replaceable>column_names</replaceable>) AS (SELECT <replaceable>...</replaceable>) SELECT <replaceable>column_names</replaceable> FROM <replaceable>view_name</replaceable>;
 </synopsis>
       A view column name list must be specified for a recursive view.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><replaceable class="parameter">name</replaceable></term>
     <listitem>
      <para>
       The name (optionally schema-qualified) of a view to be created.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><replaceable class="parameter">column_name</replaceable></term>
     <listitem>
      <para>
       An optional list of names to be used for columns of the view.
       If not given, the column names are deduced from the query.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><literal>WITH ( <replaceable class="parameter">view_option_name</replaceable> [= <replaceable class="parameter">view_option_value</replaceable>] [, ... ] )</literal></term>
     <listitem>
      <para>
       This clause specifies optional parameters for a view; the following
       parameters are supported:

       <variablelist>
        <varlistentry>
         <term><literal>check_option</literal> (<type>enum</type>)</term>
         <listitem>
          <para>
           This parameter may be either <literal>local</literal> or
           <literal>cascaded</literal>, and is equivalent to specifying
           <literal>WITH [ CASCADED | LOCAL ] CHECK OPTION</literal> (see below).
           This option can be changed on existing views using <link
           linkend="sql-alterview"><command>ALTER VIEW</command></link>.
          </para>
         </listitem>
        </varlistentry>

        <varlistentry>
         <term><literal>security_barrier</literal> (<type>boolean</type>)</term>
         <listitem>
          <para>
           This should be used if the view is intended to provide row-level
           security.  See <xref linkend="rules-privileges"/> for full details.
          </para>
         </listitem>
        </varlistentry>
       </variablelist></para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><replaceable class="parameter">query</replaceable></term>
     <listitem>
      <para>
       A <link linkend="sql-select"><command>SELECT</command></link> or
       <link linkend="sql-values"><command>VALUES</command></link> command
       which will provide the columns and rows of the view.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><literal>WITH [ CASCADED | LOCAL ] CHECK OPTION</literal>
       <indexterm zone="sql-createview">
        <primary>CHECK OPTION</primary>
       </indexterm>
       <indexterm zone="sql-createview">
        <primary>WITH CHECK OPTION</primary>
       </indexterm>
     </term>
     <listitem>
      <para>
       This option controls the behavior of automatically updatable views.  When
       this option is specified, <command>INSERT</command> and <command>UPDATE</command>
       commands on the view will be checked to ensure that new rows satisfy the
       view-defining condition (that is, the new rows are checked to ensure that
       they are visible through the view).  If they are not, the update will be
       rejected.  If the <literal>CHECK OPTION</literal> is not specified,
       <command>INSERT</command> and <command>UPDATE</command> commands on the view are
       allowed to create rows that are not visible through the view.  The
       following check options are supported:

       <variablelist>
        <varlistentry>
         <term><literal>LOCAL</literal></term>
         <listitem>
          <para>
           New rows are only checked against the conditions defined directly in
           the view itself.  Any conditions defined on underlying base views are
           not checked (unless they also specify the <literal>CHECK OPTION</literal>).
          </para>
         </listitem>
        </varlistentry>

        <varlistentry>
         <term><literal>CASCADED</literal></term>
         <listitem>
          <para>
           New rows are checked against the conditions of the view and all
           underlying base views.  If the <literal>CHECK OPTION</literal> is specified,
           and neither <literal>LOCAL</literal> nor <literal>CASCADED</literal> is specified,
           then <literal>CASCADED</literal> is assumed.
          </para>
         </listitem>
        </varlistentry>
       </variablelist>
      </para>

      <para>
       The <literal>CHECK OPTION</literal> may not be used with <literal>RECURSIVE</literal>
       views.
      </para>

      <para>
       Note that the <literal>CHECK OPTION</literal> is only supported on views that
       are automatically updatable, and do not have <literal>INSTEAD OF</literal>
       triggers or <literal>INSTEAD</literal> rules.  If an automatically updatable
       view is defined on top of a base view that has <literal>INSTEAD OF</literal>
       triggers, then the <literal>LOCAL CHECK OPTION</literal> may be used to check
       the conditions on the automatically updatable view, but the conditions
       on the base view with <literal>INSTEAD OF</literal> triggers will not be
       checked (a cascaded check option will not cascade down to a
       trigger-updatable view, and any check options defined directly on a
       trigger-updatable view will be ignored).  If the view or any of its base
       relations has an <literal>INSTEAD</literal> rule that causes the
       <command>INSERT</command> or <command>UPDATE</command> command to be rewritten, then
       all check options will be ignored in the rewritten query, including any
       checks from automatically updatable views defined on top of the relation
       with the <literal>INSTEAD</literal> rule.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </refsect1>

  <refsect1>
   <title>Notes</title>

    <para>
     Use the <link linkend="sql-dropview"><command>DROP VIEW</command></link>
     statement to drop views.
    </para>

    <para>
     Be careful that the names and types of the view's columns will be
     assigned the way you want.  For example:
 <programlisting>
 CREATE VIEW vista AS SELECT 'Hello World';
 </programlisting>
     is bad form because the column name defaults to <literal>?column?</literal>;
     also, the column data type defaults to <type>text</type>, which might not
     be what you wanted.  Better style for a string literal in a view's
     result is something like:
 <programlisting>
 CREATE VIEW vista AS SELECT text 'Hello World' AS hello;
 </programlisting>
    </para>

    <para>
     Access to tables referenced in the view is determined by permissions of
     the view owner.  In some cases, this can be used to provide secure but
     restricted access to the underlying tables.  However, not all views are
     secure against tampering; see <xref linkend="rules-privileges"/> for
     details.  Functions called in the view are treated the same as if they had
     been called directly from the query using the view.  Therefore the user of
     a view must have permissions to call all functions used by the view.
    </para>

    <para>
     When <command>CREATE OR REPLACE VIEW</command> is used on an
     existing view, only the view's defining SELECT rule is changed.
     Other view properties, including ownership, permissions, and non-SELECT
     rules, remain unchanged.  You must own the view
     to replace it (this includes being a member of the owning role).
    </para>

   <refsect2 id="sql-createview-updatable-views">
    <title>Updatable Views</title>

    <indexterm zone="sql-createview-updatable-views">
     <primary>updatable views</primary>
    </indexterm>

    <para>
     Simple views are automatically updatable: the system will allow
     <command>INSERT</command>, <command>UPDATE</command> and <command>DELETE</command> statements
     to be used on the view in the same way as on a regular table.  A view is
     automatically updatable if it satisfies all of the following conditions:

     <itemizedlist>
      <listitem>
       <para>
        The view must have exactly one entry in its <literal>FROM</literal> list,
        which must be a table or another updatable view.
       </para>
      </listitem>

      <listitem>
       <para>
        The view definition must not contain <literal>WITH</literal>,
        <literal>DISTINCT</literal>, <literal>GROUP BY</literal>, <literal>HAVING</literal>,
        <literal>LIMIT</literal>, or <literal>OFFSET</literal> clauses at the top level.
       </para>
      </listitem>

      <listitem>
       <para>
        The view definition must not contain set operations (<literal>UNION</literal>,
        <literal>INTERSECT</literal> or <literal>EXCEPT</literal>) at the top level.
       </para>
      </listitem>

      <listitem>
       <para>
        The view's select list must not contain any aggregates, window functions
        or set-returning functions.
       </para>
      </listitem>
     </itemizedlist>
    </para>

    <para>
     An automatically updatable view may contain a mix of updatable and
     non-updatable columns.  A column is updatable if it is a simple reference
     to an updatable column of the underlying base relation; otherwise the
     column is read-only, and an error will be raised if an <command>INSERT</command>
     or <command>UPDATE</command> statement attempts to assign a value to it.
    </para>

    <para>
     If the view is automatically updatable the system will convert any
     <command>INSERT</command>, <command>UPDATE</command> or <command>DELETE</command> statement
     on the view into the corresponding statement on the underlying base
     relation.  <command>INSERT</command> statements that have an <literal>ON
     CONFLICT UPDATE</literal> clause are fully supported.
    </para>

    <para>
     If an automatically updatable view contains a <literal>WHERE</literal>
     condition, the condition restricts which rows of the base relation are
     available to be modified by <command>UPDATE</command> and <command>DELETE</command>
     statements on the view.  However, an <command>UPDATE</command> is allowed to
     change a row so that it no longer satisfies the <literal>WHERE</literal>
     condition, and thus is no longer visible through the view.  Similarly,
     an <command>INSERT</command> command can potentially insert base-relation rows
     that do not satisfy the <literal>WHERE</literal> condition and thus are not
     visible through the view (<literal>ON CONFLICT UPDATE</literal> may
     similarly affect an existing row not visible through the view).
     The <literal>CHECK OPTION</literal> may be used to prevent
     <command>INSERT</command> and <command>UPDATE</command> commands from creating
     such rows that are not visible through the view.
    </para>

    <para>
     If an automatically updatable view is marked with the
     <literal>security_barrier</literal> property then all the view's <literal>WHERE</literal>
     conditions (and any conditions using operators which are marked as <literal>LEAKPROOF</literal>)
     will always be evaluated before any conditions that a user of the view has
     added.   See <xref linkend="rules-privileges"/> for full details.  Note that,
     due to this, rows which are not ultimately returned (because they do not
     pass the user's <literal>WHERE</literal> conditions) may still end up being locked.
     <command>EXPLAIN</command> can be used to see which conditions are
     applied at the relation level (and therefore do not lock rows) and which are
     not.
    </para>

    <para>
     A more complex view that does not satisfy all these conditions is
     read-only by default: the system will not allow an insert, update, or
     delete on the view.  You can get the effect of an updatable view by
     creating <literal>INSTEAD OF</literal> triggers on the view, which must
     convert attempted inserts, etc. on the view into appropriate actions
     on other tables.  For more information see <xref
     linkend="sql-createtrigger"/>.  Another possibility is to create rules
     (see <xref linkend="sql-createrule"/>), but in practice triggers are
     easier to understand and use correctly.
    </para>

    <para>
     Note that the user performing the insert, update or delete on the view
     must have the corresponding insert, update or delete privilege on the
     view.  In addition the view's owner must have the relevant privileges on
     the underlying base relations, but the user performing the update does
     not need any permissions on the underlying base relations (see
     <xref linkend="rules-privileges"/>).
    </para>
   </refsect2>
  </refsect1>

  <refsect1>
   <title>Examples</title>

   <para>
    Create a view consisting of all comedy films:

 <programlisting>
 CREATE VIEW comedies AS
     SELECT *
     FROM films
     WHERE kind = 'Comedy';
 </programlisting>
    This will create a view containing the columns that are in the
    <literal>film</literal> table at the time of view creation.  Though
    <literal>*</literal> was used to create the view, columns added later to
    the table will not be part of the view.
   </para>

   <para>
    Create a view with <literal>LOCAL CHECK OPTION</literal>:

 <programlisting>
 CREATE VIEW universal_comedies AS
     SELECT *
     FROM comedies
     WHERE classification = 'U'
     WITH LOCAL CHECK OPTION;
 </programlisting>
    This will create a view based on the <literal>comedies</literal> view, showing
    only films with <literal>kind = 'Comedy'</literal> and
    <literal>classification = 'U'</literal>. Any attempt to <command>INSERT</command> or
    <command>UPDATE</command> a row in the view will be rejected if the new row
    doesn't have <literal>classification = 'U'</literal>, but the film
    <literal>kind</literal> will not be checked.
   </para>

   <para>
    Create a view with <literal>CASCADED CHECK OPTION</literal>:

 <programlisting>
 CREATE VIEW pg_comedies AS
     SELECT *
     FROM comedies
     WHERE classification = 'PG'
     WITH CASCADED CHECK OPTION;
 </programlisting>
    This will create a view that checks both the <literal>kind</literal> and
    <literal>classification</literal> of new rows.
   </para>

   <para>
    Create a view with a mix of updatable and non-updatable columns:

 <programlisting>
 CREATE VIEW comedies AS
     SELECT f.*,
            country_code_to_name(f.country_code) AS country,
            (SELECT avg(r.rating)
             FROM user_ratings r
             WHERE r.film_id = f.id) AS avg_rating
     FROM films f
     WHERE f.kind = 'Comedy';
 </programlisting>
    This view will support <command>INSERT</command>, <command>UPDATE</command> and
    <command>DELETE</command>.  All the columns from the <literal>films</literal> table will
    be updatable, whereas the computed columns <literal>country</literal> and
    <literal>avg_rating</literal> will be read-only.
   </para>

   <para>
    Create a recursive view consisting of the numbers from 1 to 100:
 <programlisting>
 CREATE RECURSIVE VIEW public.nums_1_100 (n) AS
     VALUES (1)
 UNION ALL
     SELECT n+1 FROM nums_1_100 WHERE n &lt; 100;
 </programlisting>
    Notice that although the recursive view's name is schema-qualified in this
    <command>CREATE</command>, its internal self-reference is not schema-qualified.
    This is because the implicitly-created CTE's name cannot be
    schema-qualified.
   </para>
  </refsect1>

  <refsect1>
   <title>Compatibility</title>

   <para>
    <command>CREATE OR REPLACE VIEW</command> is a
    <productname>PostgreSQL</productname> language extension.
    So is the concept of a temporary view.
    The <literal>WITH ( ... )</literal> clause is an extension as well.
   </para>
  </refsect1>

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

   <simplelist type="inline">
    <member><xref linkend="sql-alterview"/></member>
    <member><xref linkend="sql-dropview"/></member>
    <member><xref linkend="sql-creatematerializedview"/></member>
   </simplelist>
  </refsect1>
 </refentry>
	<!--
	doc/src/sgml/ref/create_view.sgml
	PostgreSQL documentation
	-->

	<refentry id="sql-createview">
	<indexterm zone="sql-createview">
	<primary>CREATE VIEW</primary>
	</indexterm>

	<refmeta>
	<refentrytitle>CREATE VIEW</refentrytitle>
	<manvolnum>7</manvolnum>
	<refmiscinfo>SQL - Language Statements</refmiscinfo>
	</refmeta>

	<refnamediv>
	<refname>CREATE VIEW</refname>
	<refpurpose>define a new view</refpurpose>
	</refnamediv>

	<refsynopsisdiv>
	<synopsis>
	CREATE [ OR REPLACE ] [ TEMP \| TEMPORARY ] [ RECURSIVE ] VIEW <replaceable class="parameter">name</replaceable> [ ( <replaceable class="parameter">column_name</replaceable> [, ...] ) ]
	[ WITH ( <replaceable class="parameter">view_option_name</replaceable> [= <replaceable class="parameter">view_option_value</replaceable>] [, ... ] ) ]
	AS <replaceable class="parameter">query</replaceable>
	[ WITH [ CASCADED \| LOCAL ] CHECK OPTION ]
	</synopsis>
	</refsynopsisdiv>

	<refsect1>
	<title>Description</title>

	<para>
	<command>CREATE VIEW</command> defines a view of a query. The view
	is not physically materialized. Instead, the query is run every time
	the view is referenced in a query.
	</para>

	<para>
	<command>CREATE OR REPLACE VIEW</command> is similar, but if a view
	of the same name already exists, it is replaced. The new query must
	generate the same columns that were generated by the existing view query
	(that is, the same column names in the same order and with the same data
	types), but it may add additional columns to the end of the list. The
	calculations giving rise to the output columns may be completely different.
	</para>

	<para>
	If a schema name is given (for example, <literal>CREATE VIEW
	myschema.myview ...</literal>) then the view is created in the specified
	schema. Otherwise it is created in the current schema. Temporary
	views exist in a special schema, so a schema name cannot be given
	when creating a temporary view. The name of the view must be
	distinct from the name of any other view, table, sequence, index or foreign table
	in the same schema.
	</para>
	</refsect1>

	<refsect1>
	<title>Parameters</title>

	<variablelist>
	<varlistentry>
	<term><literal>TEMPORARY</literal> or <literal>TEMP</literal></term>
	<listitem>
	<para>
	If specified, the view is created as a temporary view.
	Temporary views are automatically dropped at the end of the
	current session. Existing
	permanent relations with the same name are not visible to the
	current session while the temporary view exists, unless they are
	referenced with schema-qualified names.
	</para>

	<para>
	If any of the tables referenced by the view are temporary,
	the view is created as a temporary view (whether
	<literal>TEMPORARY</literal> is specified or not).
	</para>
	</listitem>
	</varlistentry>

	<varlistentry>
	<term><literal>RECURSIVE</literal>
	<indexterm zone="sql-createview">
	<primary>RECURSIVE</primary>
	<secondary>in views</secondary>
	</indexterm>
	</term>
	<listitem>
	<para>
	Creates a recursive view. The syntax
	<synopsis>
	CREATE RECURSIVE VIEW [ <replaceable>schema</replaceable> . ] <replaceable>view_name</replaceable> (<replaceable>column_names</replaceable>) AS SELECT <replaceable>...</replaceable>;
	</synopsis>
	is equivalent to
	<synopsis>
	CREATE VIEW [ <replaceable>schema</replaceable> . ] <replaceable>view_name</replaceable> AS WITH RECURSIVE <replaceable>view_name</replaceable> (<replaceable>column_names</replaceable>) AS (SELECT <replaceable>...</replaceable>) SELECT <replaceable>column_names</replaceable> FROM <replaceable>view_name</replaceable>;
	</synopsis>
	A view column name list must be specified for a recursive view.
	</para>
	</listitem>
	</varlistentry>

	<varlistentry>
	<term><replaceable class="parameter">name</replaceable></term>
	<listitem>
	<para>
	The name (optionally schema-qualified) of a view to be created.
	</para>
	</listitem>
	</varlistentry>

	<varlistentry>
	<term><replaceable class="parameter">column_name</replaceable></term>
	<listitem>
	<para>
	An optional list of names to be used for columns of the view.
	If not given, the column names are deduced from the query.
	</para>
	</listitem>
	</varlistentry>

	<varlistentry>
	<term><literal>WITH ( <replaceable class="parameter">view_option_name</replaceable> [= <replaceable class="parameter">view_option_value</replaceable>] [, ... ] )</literal></term>
	<listitem>
	<para>
	This clause specifies optional parameters for a view; the following
	parameters are supported:

	<variablelist>
	<varlistentry>
	<term><literal>check_option</literal> (<type>enum</type>)</term>
	<listitem>
	<para>
	This parameter may be either <literal>local</literal> or
	<literal>cascaded</literal>, and is equivalent to specifying
	<literal>WITH [ CASCADED \| LOCAL ] CHECK OPTION</literal> (see below).
	This option can be changed on existing views using <link
	linkend="sql-alterview"><command>ALTER VIEW</command></link>.
	</para>
	</listitem>
	</varlistentry>

	<varlistentry>
	<term><literal>security_barrier</literal> (<type>boolean</type>)</term>
	<listitem>
	<para>
	This should be used if the view is intended to provide row-level
	security. See <xref linkend="rules-privileges"/> for full details.
	</para>
	</listitem>
	</varlistentry>
	</variablelist></para>
	</listitem>
	</varlistentry>

	<varlistentry>
	<term><replaceable class="parameter">query</replaceable></term>
	<listitem>
	<para>
	A <link linkend="sql-select"><command>SELECT</command></link> or
	<link linkend="sql-values"><command>VALUES</command></link> command
	which will provide the columns and rows of the view.
	</para>
	</listitem>
	</varlistentry>

	<varlistentry>
	<term><literal>WITH [ CASCADED \| LOCAL ] CHECK OPTION</literal>
	<indexterm zone="sql-createview">
	<primary>CHECK OPTION</primary>
	</indexterm>
	<indexterm zone="sql-createview">
	<primary>WITH CHECK OPTION</primary>
	</indexterm>
	</term>
	<listitem>
	<para>
	This option controls the behavior of automatically updatable views. When
	this option is specified, <command>INSERT</command> and <command>UPDATE</command>
	commands on the view will be checked to ensure that new rows satisfy the
	view-defining condition (that is, the new rows are checked to ensure that
	they are visible through the view). If they are not, the update will be
	rejected. If the <literal>CHECK OPTION</literal> is not specified,
	<command>INSERT</command> and <command>UPDATE</command> commands on the view are
	allowed to create rows that are not visible through the view. The
	following check options are supported:

	<variablelist>
	<varlistentry>
	<term><literal>LOCAL</literal></term>
	<listitem>
	<para>
	New rows are only checked against the conditions defined directly in
	the view itself. Any conditions defined on underlying base views are
	not checked (unless they also specify the <literal>CHECK OPTION</literal>).
	</para>
	</listitem>
	</varlistentry>

	<varlistentry>
	<term><literal>CASCADED</literal></term>
	<listitem>
	<para>
	New rows are checked against the conditions of the view and all
	underlying base views. If the <literal>CHECK OPTION</literal> is specified,
	and neither <literal>LOCAL</literal> nor <literal>CASCADED</literal> is specified,
	then <literal>CASCADED</literal> is assumed.
	</para>
	</listitem>
	</varlistentry>
	</variablelist>
	</para>

	<para>
	The <literal>CHECK OPTION</literal> may not be used with <literal>RECURSIVE</literal>
	views.
	</para>

	<para>
	Note that the <literal>CHECK OPTION</literal> is only supported on views that
	are automatically updatable, and do not have <literal>INSTEAD OF</literal>
	triggers or <literal>INSTEAD</literal> rules. If an automatically updatable
	view is defined on top of a base view that has <literal>INSTEAD OF</literal>
	triggers, then the <literal>LOCAL CHECK OPTION</literal> may be used to check
	the conditions on the automatically updatable view, but the conditions
	on the base view with <literal>INSTEAD OF</literal> triggers will not be
	checked (a cascaded check option will not cascade down to a
	trigger-updatable view, and any check options defined directly on a
	trigger-updatable view will be ignored). If the view or any of its base
	relations has an <literal>INSTEAD</literal> rule that causes the
	<command>INSERT</command> or <command>UPDATE</command> command to be rewritten, then
	all check options will be ignored in the rewritten query, including any
	checks from automatically updatable views defined on top of the relation
	with the <literal>INSTEAD</literal> rule.
	</para>
	</listitem>
	</varlistentry>
	</variablelist>
	</refsect1>

	<refsect1>
	<title>Notes</title>

	<para>
	Use the <link linkend="sql-dropview"><command>DROP VIEW</command></link>
	statement to drop views.
	</para>

	<para>
	Be careful that the names and types of the view's columns will be
	assigned the way you want. For example:
	<programlisting>
	CREATE VIEW vista AS SELECT 'Hello World';
	</programlisting>
	is bad form because the column name defaults to <literal>?column?</literal>;
	also, the column data type defaults to <type>text</type>, which might not
	be what you wanted. Better style for a string literal in a view's
	result is something like:
	<programlisting>
	CREATE VIEW vista AS SELECT text 'Hello World' AS hello;
	</programlisting>
	</para>

	<para>
	Access to tables referenced in the view is determined by permissions of
	the view owner. In some cases, this can be used to provide secure but
	restricted access to the underlying tables. However, not all views are
	secure against tampering; see <xref linkend="rules-privileges"/> for
	details. Functions called in the view are treated the same as if they had
	been called directly from the query using the view. Therefore the user of
	a view must have permissions to call all functions used by the view.
	</para>

	<para>
	When <command>CREATE OR REPLACE VIEW</command> is used on an
	existing view, only the view's defining SELECT rule is changed.
	Other view properties, including ownership, permissions, and non-SELECT
	rules, remain unchanged. You must own the view
	to replace it (this includes being a member of the owning role).
	</para>

	<refsect2 id="sql-createview-updatable-views">
	<title>Updatable Views</title>

	<indexterm zone="sql-createview-updatable-views">
	<primary>updatable views</primary>
	</indexterm>

	<para>
	Simple views are automatically updatable: the system will allow
	<command>INSERT</command>, <command>UPDATE</command> and <command>DELETE</command> statements
	to be used on the view in the same way as on a regular table. A view is
	automatically updatable if it satisfies all of the following conditions:

	<itemizedlist>
	<listitem>
	<para>
	The view must have exactly one entry in its <literal>FROM</literal> list,
	which must be a table or another updatable view.
	</para>
	</listitem>

	<listitem>
	<para>
	The view definition must not contain <literal>WITH</literal>,
	<literal>DISTINCT</literal>, <literal>GROUP BY</literal>, <literal>HAVING</literal>,
	<literal>LIMIT</literal>, or <literal>OFFSET</literal> clauses at the top level.
	</para>
	</listitem>

	<listitem>
	<para>
	The view definition must not contain set operations (<literal>UNION</literal>,
	<literal>INTERSECT</literal> or <literal>EXCEPT</literal>) at the top level.
	</para>
	</listitem>

	<listitem>
	<para>
	The view's select list must not contain any aggregates, window functions
	or set-returning functions.
	</para>
	</listitem>
	</itemizedlist>
	</para>

	<para>
	An automatically updatable view may contain a mix of updatable and
	non-updatable columns. A column is updatable if it is a simple reference
	to an updatable column of the underlying base relation; otherwise the
	column is read-only, and an error will be raised if an <command>INSERT</command>
	or <command>UPDATE</command> statement attempts to assign a value to it.
	</para>

	<para>
	If the view is automatically updatable the system will convert any
	<command>INSERT</command>, <command>UPDATE</command> or <command>DELETE</command> statement
	on the view into the corresponding statement on the underlying base
	relation. <command>INSERT</command> statements that have an <literal>ON
	CONFLICT UPDATE</literal> clause are fully supported.
	</para>

	<para>
	If an automatically updatable view contains a <literal>WHERE</literal>
	condition, the condition restricts which rows of the base relation are
	available to be modified by <command>UPDATE</command> and <command>DELETE</command>
	statements on the view. However, an <command>UPDATE</command> is allowed to
	change a row so that it no longer satisfies the <literal>WHERE</literal>
	condition, and thus is no longer visible through the view. Similarly,
	an <command>INSERT</command> command can potentially insert base-relation rows
	that do not satisfy the <literal>WHERE</literal> condition and thus are not
	visible through the view (<literal>ON CONFLICT UPDATE</literal> may
	similarly affect an existing row not visible through the view).
	The <literal>CHECK OPTION</literal> may be used to prevent
	<command>INSERT</command> and <command>UPDATE</command> commands from creating
	such rows that are not visible through the view.
	</para>

	<para>
	If an automatically updatable view is marked with the
	<literal>security_barrier</literal> property then all the view's <literal>WHERE</literal>
	conditions (and any conditions using operators which are marked as <literal>LEAKPROOF</literal>)
	will always be evaluated before any conditions that a user of the view has
	added. See <xref linkend="rules-privileges"/> for full details. Note that,
	due to this, rows which are not ultimately returned (because they do not
	pass the user's <literal>WHERE</literal> conditions) may still end up being locked.
	<command>EXPLAIN</command> can be used to see which conditions are
	applied at the relation level (and therefore do not lock rows) and which are
	not.
	</para>

	<para>
	A more complex view that does not satisfy all these conditions is
	read-only by default: the system will not allow an insert, update, or
	delete on the view. You can get the effect of an updatable view by
	creating <literal>INSTEAD OF</literal> triggers on the view, which must
	convert attempted inserts, etc. on the view into appropriate actions
	on other tables. For more information see <xref
	linkend="sql-createtrigger"/>. Another possibility is to create rules
	(see <xref linkend="sql-createrule"/>), but in practice triggers are
	easier to understand and use correctly.
	</para>

	<para>
	Note that the user performing the insert, update or delete on the view
	must have the corresponding insert, update or delete privilege on the
	view. In addition the view's owner must have the relevant privileges on
	the underlying base relations, but the user performing the update does
	not need any permissions on the underlying base relations (see
	<xref linkend="rules-privileges"/>).
	</para>
	</refsect2>
	</refsect1>

	<refsect1>
	<title>Examples</title>

	<para>
	Create a view consisting of all comedy films:

	<programlisting>
	CREATE VIEW comedies AS
	SELECT *
	FROM films
	WHERE kind = 'Comedy';
	</programlisting>
	This will create a view containing the columns that are in the
	<literal>film</literal> table at the time of view creation. Though
	<literal>*</literal> was used to create the view, columns added later to
	the table will not be part of the view.
	</para>

	<para>
	Create a view with <literal>LOCAL CHECK OPTION</literal>:

	<programlisting>
	CREATE VIEW universal_comedies AS
	SELECT *
	FROM comedies
	WHERE classification = 'U'
	WITH LOCAL CHECK OPTION;
	</programlisting>
	This will create a view based on the <literal>comedies</literal> view, showing
	only films with <literal>kind = 'Comedy'</literal> and
	<literal>classification = 'U'</literal>. Any attempt to <command>INSERT</command> or
	<command>UPDATE</command> a row in the view will be rejected if the new row
	doesn't have <literal>classification = 'U'</literal>, but the film
	<literal>kind</literal> will not be checked.
	</para>

	<para>
	Create a view with <literal>CASCADED CHECK OPTION</literal>:

	<programlisting>
	CREATE VIEW pg_comedies AS
	SELECT *
	FROM comedies
	WHERE classification = 'PG'
	WITH CASCADED CHECK OPTION;
	</programlisting>
	This will create a view that checks both the <literal>kind</literal> and
	<literal>classification</literal> of new rows.
	</para>

	<para>
	Create a view with a mix of updatable and non-updatable columns:

	<programlisting>
	CREATE VIEW comedies AS
	SELECT f.*,
	country_code_to_name(f.country_code) AS country,
	(SELECT avg(r.rating)
	FROM user_ratings r
	WHERE r.film_id = f.id) AS avg_rating
	FROM films f
	WHERE f.kind = 'Comedy';
	</programlisting>
	This view will support <command>INSERT</command>, <command>UPDATE</command> and
	<command>DELETE</command>. All the columns from the <literal>films</literal> table will
	be updatable, whereas the computed columns <literal>country</literal> and
	<literal>avg_rating</literal> will be read-only.
	</para>

	<para>
	Create a recursive view consisting of the numbers from 1 to 100:
	<programlisting>
	CREATE RECURSIVE VIEW public.nums_1_100 (n) AS
	VALUES (1)
	UNION ALL
	SELECT n+1 FROM nums_1_100 WHERE n < 100;
	</programlisting>
	Notice that although the recursive view's name is schema-qualified in this
	<command>CREATE</command>, its internal self-reference is not schema-qualified.
	This is because the implicitly-created CTE's name cannot be
	schema-qualified.
	</para>
	</refsect1>

	<refsect1>
	<title>Compatibility</title>

	<para>
	<command>CREATE OR REPLACE VIEW</command> is a
	<productname>PostgreSQL</productname> language extension.
	So is the concept of a temporary view.
	The <literal>WITH ( ... )</literal> clause is an extension as well.
	</para>
	</refsect1>

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

	<simplelist type="inline">
	<member><xref linkend="sql-alterview"/></member>
	<member><xref linkend="sql-dropview"/></member>
	<member><xref linkend="sql-creatematerializedview"/></member>
	</simplelist>
	</refsect1>
	</refentry>