0845b6f326
> > comma). > > OK. But the documentation implies there is a comma, so it should probably > get chenged then. Yes, it should. (attached) [ Backpatched to 7.3.X too.] Rod Taylor
250 lines
6.8 KiB
Plaintext
250 lines
6.8 KiB
Plaintext
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$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_domain.sgml,v 1.11 2003/02/13 05:32:42 momjian Exp $
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PostgreSQL documentation
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-->
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<refentry id="SQL-CREATEDOMAIN">
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<refmeta>
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<refentrytitle id="sql-createdomain-title">
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CREATE DOMAIN
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</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 DOMAIN
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</refname>
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<refpurpose>
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define a new domain
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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>2002-02-24</date>
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</refsynopsisdivinfo>
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<synopsis>
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CREATE DOMAIN <replaceable class="parameter">domainname</replaceable> [AS] <replaceable class="parameter">data_type</replaceable>
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[ DEFAULT <replaceable>default_expr</> ]
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[ <replaceable class="PARAMETER">constraint</replaceable> [ ... ] ]
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where <replaceable class="PARAMETER">constraint</replaceable> is:
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[ CONSTRAINT <replaceable class="PARAMETER">constraint_name</replaceable> ]
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{ NOT NULL | NULL | CHECK (<replaceable class="PARAMETER">expression</replaceable>) }
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</synopsis>
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<refsect2 id="R2-SQL-CREATEDOMAIN-1">
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<refsect2info>
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<date>2002-02-24</date>
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</refsect2info>
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<title>
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Parameters
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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">domainname</replaceable></term>
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<listitem>
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<para>
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The name (optionally schema-qualified) of a domain 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">data_type</replaceable></term>
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<listitem>
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<para>
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The underlying data type of the domain. This may include array
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specifiers.
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Refer to the &cite-user; for further
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information about data types and arrays.
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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>DEFAULT
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<replaceable>default_expr</replaceable></literal></term>
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<listitem>
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<para>
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The <literal>DEFAULT</> clause specifies a default value for
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columns of the domain data type. The value
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is any variable-free expression (but subselects are not allowed).
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The
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data type of the default expression must match the data type of the
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domain.
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</para>
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<para>
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The default expression will be used in any insert operation that
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does not specify a value for the column. If there is no default
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for a domain, then the default is NULL.
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</para>
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<note>
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<para>
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If a default value is specified for a particular column, it
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overrides any default associated with the domain. In turn,
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the domain default overrides any default value associated with
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the underlying data type.
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</para>
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</note>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>CONSTRAINT <replaceable class="PARAMETER">constraint_name</replaceable></literal></term>
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<listitem>
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<para>
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An optional name for a constraint. If not specified,
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the system generates a name.
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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>NOT NULL</></term>
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<listitem>
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<para>
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Values of this domain are not allowed to be NULL.
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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>NULL</></term>
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<listitem>
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<para>
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Values of this domain are allowed to be NULL. This is the default.
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</para>
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<para>
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This clause is only available for compatibility with
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non-standard SQL databases. Its use is discouraged in new
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applications.
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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>CHECK (<replaceable class="PARAMETER">expression</replaceable>)</literal></term>
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<listitem>
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<para>
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<literal>CHECK</> clauses specify integrity constraints or tests
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which values of the domain must satisfy.
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Each constraint must be an expression
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producing a Boolean result. It should use the name <literal>VALUE</>
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to refer to the value being tested.
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</para>
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<para>
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Currently, <literal>CHECK</literal> expressions cannot contain
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subselects nor refer to variables other than <literal>VALUE</>.
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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-CREATEDOMAIN-2">
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<refsect2info>
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<date>2002-02-24</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 DOMAIN
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</computeroutput></term>
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<listitem>
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<para>
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Message returned if the domain is successfully created.
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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-CREATEDOMAIN-1">
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<refsect1info>
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<date>2002-02-24</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 DOMAIN</command> allows the user to register a new
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data domain with <productname>PostgreSQL</> for use in the
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current data base. The user who defines a domain becomes its owner.
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</para>
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<para>
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If a schema name is given (for example, <literal>CREATE DOMAIN
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myschema.mydomain ...</>) then the domain 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 domain name must be unique among the types and domains existing
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in its schema.
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</para>
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<para>
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Domains are useful for abstracting common fields between tables into
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a single location for maintenance. An email address column may be used
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in several tables, all with the same properties. Define a domain and
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use that rather than setting up each table's constraints individually.
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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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This example creates the <type>country_code</type> data type and then uses the
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type in a table definition:
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<programlisting>
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CREATE DOMAIN country_code char(2) NOT NULL;
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CREATE TABLE countrylist (id INT4, country country_code);
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</programlisting>
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</para>
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</refsect1>
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<refsect1 id="SQL-CREATEDOMAIN-see-also">
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<title>See Also</title>
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<simplelist type="inline">
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<member><xref linkend="sql-dropdomain" endterm="sql-dropdomain-title"></member>
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<member>&cite-programmer;</member>
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</simplelist>
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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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