path: root/doc/src/sgml/ref/create_view.sgml

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<refentry id="SQL-CREATEVIEW">
 <refmeta>
  <refentrytitle id="SQL-CREATEVIEW-TITLE">CREATE VIEW</refentrytitle>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>
 <refnamediv>
  <refname>
   CREATE VIEW
  </refname>
  <refpurpose>
   define a new view
  </refpurpose>
 </refnamediv>
 <refsynopsisdiv>
  <refsynopsisdivinfo>
   <date>2000-03-25</date>
  </refsynopsisdivinfo>
  <synopsis>
CREATE [ OR REPLACE ] VIEW <replaceable class="PARAMETER">view</replaceable> [ ( <replaceable
class="PARAMETER">column name list</replaceable> ) ] AS SELECT <replaceable class="PARAMETER">query</replaceable>
  </synopsis>

  <refsect2 id="R2-SQL-CREATEVIEW-1">
   <refsect2info> 
    <date>2000-03-25</date>
   </refsect2info>
   <title>
    Inputs
   </title>
   <para>

    <variablelist>
     <varlistentry>
      <term><replaceable class="parameter">view</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 list</replaceable></term>
      <listitem>
       <para>
        An optional list of names to be used for columns of the view.
	If given, these names override the column names that would be
	deduced from the SQL query.
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term><replaceable class="parameter">query</replaceable></term>
      <listitem>
       <para>
	An SQL query (that is, a <command>SELECT</> statement)
	which will provide the columns and rows of the view.
       </para>
       <para>
	Refer to <xref linkend="sql-select" endterm="sql-select-title"> for more information
	about valid arguments.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>
  </refsect2>

  <refsect2 id="R2-SQL-CREATEVIEW-2">
   <refsect2info>
    <date>2000-03-25</date>
   </refsect2info>
   <title>
    Outputs
   </title>
   <para>
    <variablelist>
     <varlistentry>
      <term><computeroutput>
CREATE VIEW
       </computeroutput></term>
      <listitem>
       <para>
	The message returned if the view is successfully created.
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term><computeroutput>
ERROR:  Relation '<replaceable class="parameter">view</replaceable>' already exists
       </computeroutput></term>
      <listitem>
       <para>
	This error occurs if the view specified already exists in the database.
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term><computeroutput>
WARNING:  Attribute '<replaceable class="parameter">column</replaceable>' has an unknown type
       </computeroutput></term>
      <listitem>
       <para>
	The view will be created having a column with an unknown type
	if you do not specify it. For example, the following command gives
	a warning:
	<programlisting>
CREATE VIEW vista AS SELECT 'Hello World'
	</programlisting>

	whereas this command does not:

	<programlisting>
CREATE VIEW vista AS SELECT text 'Hello World'
	</programlisting>
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>
  </refsect2>
 </refsynopsisdiv>

 <refsect1 id="R1-SQL-CREATEVIEW-1">
  <refsect1info>
   <date>2000-03-25</date>
  </refsect1info>
  <title>
   Description
  </title>

  <para>
   <command>CREATE VIEW</command> defines a view of a query.
   The view is not physically materialized. Instead, a query
   rewrite rule (an <literal>ON SELECT</> rule) is automatically generated to
   support SELECT operations on views.
  </para>

  <para>
   <command>CREATE OR REPLACE VIEW</command> is similar, but if a view
   of the same name already exists, it is replaced.  You can only replace
   a view with a new query that generates the identical set of columns
   (i.e., same column names and data types).
  </para>

  <para>
   If a schema name is given (for example, <literal>CREATE VIEW
   myschema.myview ...</>) then the view is created in the
   specified schema.  Otherwise it is created in the current schema (the one
   at the front of the search path; see <literal>CURRENT_SCHEMA()</>).
   The view name must be distinct from the name of any other view, table,
   sequence, or index in the same schema.
  </para>

  <refsect2 id="R2-SQL-CREATEVIEW-3">
   <refsect2info>
    <date>2000-03-25</date>
   </refsect2info>
   <title>
    Notes
   </title>

   <para>
    Currently, views are read only: the system will not allow an insert,
    update, or delete on a view.  You can get the effect of an updatable
    view by creating rules that rewrite inserts, etc. on the view into
    appropriate actions on other tables.  For more information see
    <xref linkend="sql-createrule" endterm="sql-createrule-title">.
   </para>

   <para>
    Use the <command>DROP VIEW</command> statement to drop views.
   </para>
  </refsect2>
 </refsect1>

 <refsect1 id="R1-SQL-CREATEVIEW-2">
  <title>
   Usage
  </title>
  <para>
   Create a view consisting of all Comedy films:

   <programlisting>
CREATE VIEW kinds AS
    SELECT *
    FROM films
    WHERE kind = 'Comedy';

SELECT * FROM kinds;

 code  |           title           | did | date_prod  |  kind  | len
-------+---------------------------+-----+------------+--------+-------
 UA502 | Bananas                   | 105 | 1971-07-13 | Comedy | 01:22
 C_701 | There's a Girl in my Soup | 107 | 1970-06-11 | Comedy | 01:36
(2 rows)
   </programlisting>
  </para>
 </refsect1>
 
 <refsect1 id="R1-SQL-CREATEVIEW-3">
  <title>
   Compatibility
  </title>
  
  <refsect2 id="R2-SQL-CREATEVIEW-5">
   <refsect2info>
    <date>2000-03-25</date>
   </refsect2info>
   <title>
    SQL92
   </title>

   <para>
    SQL92 specifies some additional capabilities for the
    <command>CREATE VIEW</command> statement:
   </para>
   <synopsis>
CREATE VIEW <replaceable class="parameter">view</replaceable> [ <replaceable class="parameter">column</replaceable> [, ...] ]
    AS SELECT <replaceable class="parameter">expression</replaceable> [ AS <replaceable class="parameter">colname</replaceable> ] [, ...]
    FROM <replaceable class="parameter">table</replaceable> [ WHERE <replaceable class="parameter">condition</replaceable> ]
    [ WITH [ CASCADE | LOCAL ] CHECK OPTION ]
   </synopsis>

   <para>
    The optional clauses for the full SQL92 command are:

   <variablelist>
     <varlistentry>
      <term>CHECK OPTION</term>
      <listitem>
       <para>
	This option is to do with updatable views.
	All <command>INSERT</> and <command>UPDATE</> commands on the view will be
	checked to ensure data satisfy the view-defining
	condition. If they do not, the update will be rejected.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>LOCAL</term>
      <listitem>
       <para>
	Check for integrity on this view.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>CASCADE</term>
      <listitem>
       <para>
	Check for integrity on this view and on any dependent
	view. CASCADE is assumed if neither CASCADE nor LOCAL is specified.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>

   <para>
    <command>CREATE OR REPLACE VIEW</command> is a
    <productname>PostgreSQL</productname> language extension.
   </para>

  </refsect2>
 </refsect1>
</refentry>

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