drop_cast.sgml

postgresql8.3.4源码,开源数据库

<!-- $PostgreSQL: pgsql/doc/src/sgml/ref/drop_cast.sgml,v 1.8 2006/09/16 00:30:18 momjian Exp $ -->

<refentry id="SQL-DROPCAST">
 <refmeta>
  <refentrytitle id="SQL-DROPCAST-TITLE">DROP CAST</refentrytitle>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>

 <refnamediv>
  <refname>DROP CAST</refname>
  <refpurpose>remove a cast</refpurpose>
 </refnamediv>

 <indexterm zone="sql-dropcast">
  <primary>DROP CAST</primary>
 </indexterm>

 <refsynopsisdiv>
<synopsis>
DROP CAST [ IF EXISTS ] (<replaceable>sourcetype</replaceable> AS <replaceable>targettype</replaceable>) [ CASCADE | RESTRICT ]
</synopsis>
 </refsynopsisdiv>
  
 <refsect1 id="sql-dropcast-description">
  <title>Description</title>

  <para>
   <command>DROP CAST</command> removes a previously defined cast.
  </para>

  <para>
   To be able to drop a cast, you must own the source or the target
   data type.  These are the same privileges that are required to
   create a cast.
  </para>
 </refsect1>

 <refsect1>
  <title>Parameters</title>

   <variablelist>

   <varlistentry>
    <term><literal>IF EXISTS</literal></term>
    <listitem>
     <para>
      Do not throw an error if the cast does not exist. A notice is issued 
      in this case.
     </para>
    </listitem>
   </varlistentry>

    <varlistentry>
     <term><replaceable>sourcetype</replaceable></term>

     <listitem>
      <para>
       The name of the source data type of the cast.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><replaceable>targettype</replaceable></term>

     <listitem>
      <para>
       The name of the target data type of the cast.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><literal>CASCADE</literal></term>
     <term><literal>RESTRICT</literal></term>

     <listitem>
      <para>
       These key words do not have any effect, since there are no
       dependencies on casts.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
 </refsect1>

 <refsect1 id="sql-dropcast-examples">
  <title>Examples</title>

  <para>
   To drop the cast from type <type>text</type> to type <type>int</type>:
<programlisting>
DROP CAST (text AS int);
</programlisting>
  </para>
 </refsect1>
 
 <refsect1 id="sql-dropcast-compat">
  <title>Compatibility</title>

  <para>
   The <command>DROP CAST</command> command conforms to the SQL standard.
  </para>
 </refsect1>

 <refsect1>
  <title>See Also</title>

  <simplelist type="inline">
   <member><xref linkend="sql-createcast" endterm="sql-createcast-title"></member>
  </simplelist>
 </refsect1>

</refentry>