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b0422b215c
make VALUE a non-reserved word again, use less invasive method of passing ConstraintTestValue into transformExpr, fix problems with nested constraint testing, do correct thing with NULL result from a constraint expression, remove memory leak. Domain checks still need much more work if we are going to allow ALTER DOMAIN, however.
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 1.9 2002/12/12 20:35:07 tgl 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 <citetitle>User's Guide</citetitle> 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><citetitle>PostgreSQL Programmer's Guide</citetitle></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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