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264 lines
8.4 KiB
Plaintext
<!--
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doc/src/sgml/ref/create_view.sgml
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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>CREATE VIEW</refentrytitle>
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<manvolnum>7</manvolnum>
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<refmiscinfo>SQL - Language Statements</refmiscinfo>
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</refmeta>
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<refnamediv>
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<refname>CREATE VIEW</refname>
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<refpurpose>define a new view</refpurpose>
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</refnamediv>
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<indexterm zone="sql-createview">
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<primary>CREATE VIEW</primary>
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</indexterm>
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<refsynopsisdiv>
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<synopsis>
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CREATE [ OR REPLACE ] [ TEMP | TEMPORARY ] VIEW <replaceable class="PARAMETER">name</replaceable> [ ( <replaceable class="PARAMETER">column_name</replaceable> [, ...] ) ]
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[ WITH ( <replaceable class="PARAMETER">view_option_name</replaceable> [= <replaceable class="PARAMETER">view_option_value</replaceable>] [, ... ] ) ]
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AS <replaceable class="PARAMETER">query</replaceable>
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</synopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>
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<command>CREATE VIEW</command> defines a view of a query. The view
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is not physically materialized. Instead, the query is run every time
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the view is referenced in a query.
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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. The new query must
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generate the same columns that were generated by the existing view query
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(that is, the same column names in the same order and with the same data
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types), but it may add additional columns to the end of the list. The
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calculations giving rise to the output columns may be completely different.
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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 specified
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schema. Otherwise it is created in the current schema. Temporary
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views exist in a special schema, so a schema name cannot be given
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when creating a temporary view. The name of the view must be
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distinct from the name of any other view, table, sequence, index or foreign table
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in the same schema.
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</para>
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</refsect1>
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<refsect1>
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<title>Parameters</title>
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<variablelist>
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<varlistentry>
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<term><literal>TEMPORARY</> or <literal>TEMP</></term>
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<listitem>
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<para>
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If specified, the view is created as a temporary view.
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Temporary views are automatically dropped at the end of the
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current session. Existing
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permanent relations with the same name are not visible to the
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current session while the temporary view exists, unless they are
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referenced with schema-qualified names.
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</para>
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<para>
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If any of the tables referenced by the view are temporary,
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the view is created as a temporary view (whether
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<literal>TEMPORARY</literal> is specified or not).
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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">name</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</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 not given, the column names are deduced from the 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><literal>WITH ( <replaceable class="PARAMETER">view_option_name</replaceable> [= <replaceable class="PARAMETER">view_option_value</replaceable>] [, ... ] )</literal></term>
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<listitem>
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<para>
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This clause specifies optional parameters for a view; currently, the
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only supported parameter name is <literal>security_barrier</literal>,
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which should be enabled when a view is intended to provide row-level
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security. See <xref linkend="rules-privileges"> for full details.
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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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A <xref linkend="sql-select"> or
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<xref linkend="sql-values"> command
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which will provide the columns and rows of the view.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Notes</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 <xref linkend="sql-dropview">
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statement to drop views.
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</para>
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<para>
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Be careful that the names and types of the view's columns will be
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assigned the way you want. For example:
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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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is bad form in two ways: the column name defaults to <literal>?column?</>,
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and the column data type defaults to <type>unknown</>. If you want a
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string literal in a view's result, use something like:
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<programlisting>
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CREATE VIEW vista AS SELECT text 'Hello World' AS hello;
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</programlisting>
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</para>
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<para>
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Access to tables referenced in the view is determined by permissions of
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the view owner. In some cases, this can be used to provide secure but
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restricted access to the underlying tables. However, not all views are
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secure against tampering; see <xref linkend="rules-privileges"> for
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details. Functions called in the view are treated the same as if they had
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been called directly from the query using the view. Therefore the user of
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a view must have permissions to call all functions used by the view.
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</para>
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<para>
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When <command>CREATE OR REPLACE VIEW</> is used on an
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existing view, only the view's defining SELECT rule is changed.
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Other view properties, including ownership, permissions, and non-SELECT
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rules, remain unchanged. You must own the view
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to replace it (this includes being a member of the owning role).
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</para>
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</refsect1>
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<refsect1>
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<title>Examples</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 comedies AS
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SELECT *
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FROM films
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WHERE kind = 'Comedy';
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</programlisting>
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This will create a view containing the columns that are in the
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<literal>film</> table at the time of view creation. Though
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<literal>*</> was used to create the view, columns added later to
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the table will not be part of the view.
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</para>
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</refsect1>
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<refsect1>
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<title>Compatibility</title>
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<para>
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The SQL standard specifies some additional capabilities for the
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<command>CREATE VIEW</command> statement:
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<synopsis>
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CREATE VIEW <replaceable class="parameter">name</replaceable> [ ( <replaceable class="parameter">column_name</replaceable> [, ...] ) ]
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AS <replaceable class="PARAMETER">query</replaceable>
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[ WITH [ CASCADED | LOCAL ] CHECK OPTION ]
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</synopsis>
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</para>
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<para>
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The optional clauses for the full SQL command are:
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<variablelist>
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<varlistentry>
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<term><literal>CHECK OPTION</literal></term>
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<listitem>
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<para>
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This option has to do with updatable views. All
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<command>INSERT</> and <command>UPDATE</> commands on the view
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will be checked to ensure data satisfy the view-defining
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condition (that is, the new data would be visible through the
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view). 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><literal>LOCAL</literal></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><literal>CASCADED</literal></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. <literal>CASCADED</> is assumed if neither
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<literal>CASCADED</> nor <literal>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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So is the concept of a temporary view.
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</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<simplelist type="inline">
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<member><xref linkend="sql-alterview"></member>
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<member><xref linkend="sql-dropview"></member>
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</simplelist>
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</refsect1>
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</refentry>
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