291 lines
7.7 KiB
Plaintext
291 lines
7.7 KiB
Plaintext
<!--
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$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_view.sgml,v 1.20 2002/09/21 18:32:54 petere Exp $
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PostgreSQL documentation
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-->
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<refentry id="SQL-CREATEVIEW">
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<refmeta>
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<refentrytitle id="SQL-CREATEVIEW-TITLE">CREATE VIEW</refentrytitle>
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<refmiscinfo>SQL - Language Statements</refmiscinfo>
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</refmeta>
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<refnamediv>
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<refname>
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CREATE VIEW
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</refname>
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<refpurpose>
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define a new view
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</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<refsynopsisdivinfo>
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<date>2000-03-25</date>
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</refsynopsisdivinfo>
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<synopsis>
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CREATE [ OR REPLACE ] VIEW <replaceable class="PARAMETER">view</replaceable> [ ( <replaceable
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class="PARAMETER">column name list</replaceable> ) ] AS SELECT <replaceable class="PARAMETER">query</replaceable>
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</synopsis>
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<refsect2 id="R2-SQL-CREATEVIEW-1">
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<refsect2info>
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<date>2000-03-25</date>
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</refsect2info>
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<title>
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Inputs
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</title>
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<para>
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<variablelist>
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<varlistentry>
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<term><replaceable class="parameter">view</replaceable></term>
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<listitem>
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<para>
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The name (optionally schema-qualified) of a view to be created.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">column name list</replaceable></term>
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<listitem>
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<para>
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An optional list of names to be used for columns of the view.
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If given, these names override the column names that would be
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deduced from the SQL query.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">query</replaceable></term>
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<listitem>
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<para>
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An SQL query (that is, a <command>SELECT</> statement)
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which will provide the columns and rows of the view.
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</para>
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<para>
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Refer to <xref linkend="sql-select"> for more information
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about valid arguments.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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</refsect2>
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<refsect2 id="R2-SQL-CREATEVIEW-2">
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<refsect2info>
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<date>2000-03-25</date>
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</refsect2info>
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<title>
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Outputs
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</title>
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<para>
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<variablelist>
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<varlistentry>
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<term><computeroutput>
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CREATE VIEW
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</computeroutput></term>
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<listitem>
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<para>
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The message returned if the view is successfully created.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><computeroutput>
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ERROR: Relation '<replaceable class="parameter">view</replaceable>' already exists
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</computeroutput></term>
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<listitem>
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<para>
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This error occurs if the view specified already exists in the database.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><computeroutput>
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WARNING: Attribute '<replaceable class="parameter">column</replaceable>' has an unknown type
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</computeroutput></term>
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<listitem>
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<para>
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The view will be created having a column with an unknown type
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if you do not specify it. For example, the following command gives
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a warning:
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<programlisting>
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CREATE VIEW vista AS SELECT 'Hello World'
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</programlisting>
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whereas this command does not:
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<programlisting>
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CREATE VIEW vista AS SELECT text 'Hello World'
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</programlisting>
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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</refsect2>
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</refsynopsisdiv>
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<refsect1 id="R1-SQL-CREATEVIEW-1">
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<refsect1info>
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<date>2000-03-25</date>
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</refsect1info>
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<title>
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Description
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</title>
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<para>
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<command>CREATE VIEW</command> defines a view of a query.
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The view is not physically materialized. Instead, a query
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rewrite rule (an <literal>ON SELECT</> rule) is automatically generated to
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support SELECT operations on views.
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</para>
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<para>
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<command>CREATE OR REPLACE VIEW</command> is similar, but if a view
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of the same name already exists, it is replaced. You can only replace
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a view with a new query that generates the identical set of columns
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(i.e., same column names and data types).
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</para>
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<para>
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If a schema name is given (for example, <literal>CREATE VIEW
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myschema.myview ...</>) then the view is created in the
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specified schema. Otherwise it is created in the current schema (the one
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at the front of the search path; see <literal>CURRENT_SCHEMA()</>).
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The view name must be distinct from the name of any other view, table,
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sequence, or index in the same schema.
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</para>
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<refsect2 id="R2-SQL-CREATEVIEW-3">
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<refsect2info>
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<date>2000-03-25</date>
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</refsect2info>
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<title>
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Notes
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</title>
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<para>
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Currently, views are read only: the system will not allow an insert,
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update, or delete on a view. You can get the effect of an updatable
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view by creating rules that rewrite inserts, etc. on the view into
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appropriate actions on other tables. For more information see
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<xref linkend="sql-createrule">.
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</para>
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<para>
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Use the <command>DROP VIEW</command> statement to drop views.
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</para>
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</refsect2>
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</refsect1>
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<refsect1 id="R1-SQL-CREATEVIEW-2">
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<title>
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Usage
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</title>
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<para>
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Create a view consisting of all Comedy films:
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<programlisting>
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CREATE VIEW kinds AS
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SELECT *
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FROM films
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WHERE kind = 'Comedy';
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SELECT * FROM kinds;
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code | title | did | date_prod | kind | len
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-------+---------------------------+-----+------------+--------+-------
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UA502 | Bananas | 105 | 1971-07-13 | Comedy | 01:22
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C_701 | There's a Girl in my Soup | 107 | 1970-06-11 | Comedy | 01:36
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(2 rows)
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</programlisting>
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</para>
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</refsect1>
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<refsect1 id="R1-SQL-CREATEVIEW-3">
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<title>
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Compatibility
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</title>
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<refsect2 id="R2-SQL-CREATEVIEW-5">
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<refsect2info>
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<date>2000-03-25</date>
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</refsect2info>
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<title>
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SQL92
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</title>
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<para>
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SQL92 specifies some additional capabilities for the
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<command>CREATE VIEW</command> statement:
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</para>
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<synopsis>
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CREATE VIEW <replaceable class="parameter">view</replaceable> [ <replaceable class="parameter">column</replaceable> [, ...] ]
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AS SELECT <replaceable class="parameter">expression</replaceable> [ AS <replaceable class="parameter">colname</replaceable> ] [, ...]
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FROM <replaceable class="parameter">table</replaceable> [ WHERE <replaceable class="parameter">condition</replaceable> ]
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[ WITH [ CASCADE | LOCAL ] CHECK OPTION ]
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</synopsis>
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<para>
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The optional clauses for the full SQL92 command are:
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<variablelist>
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<varlistentry>
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<term>CHECK OPTION</term>
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<listitem>
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<para>
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This option is to do with updatable views.
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All <command>INSERT</> and <command>UPDATE</> commands on the view will be
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checked to ensure data satisfy the view-defining
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condition. If they do not, the update will be rejected.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>LOCAL</term>
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<listitem>
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<para>
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Check for integrity on this view.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>CASCADE</term>
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<listitem>
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<para>
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Check for integrity on this view and on any dependent
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view. CASCADE is assumed if neither CASCADE nor LOCAL is specified.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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<para>
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<command>CREATE OR REPLACE VIEW</command> is a
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<productname>PostgreSQL</productname> language extension.
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</para>
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</refsect2>
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</refsect1>
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</refentry>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml
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sgml-omittag:nil
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sgml-shorttag:t
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sgml-minimize-attributes:nil
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sgml-always-quote-attributes:t
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sgml-indent-step:1
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sgml-indent-data:t
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sgml-parent-document:nil
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sgml-default-dtd-file:"../reference.ced"
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sgml-exposed-tags:nil
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sgml-local-catalogs:"/usr/lib/sgml/catalog"
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sgml-local-ecat-files:nil
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End:
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-->
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