<!--
doc/src/sgml/ref/alter_type.sgml
PostgreSQL documentation
-->

<refentry id="SQL-ALTERTYPE">
 <refmeta>
  <refentrytitle>ALTER TYPE</refentrytitle>
  <manvolnum>7</manvolnum>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>

 <refnamediv>
  <refname>ALTER TYPE</refname>
  <refpurpose>
   change the definition of a type
  </refpurpose>
 </refnamediv>

 <indexterm zone="sql-altertype">
  <primary>ALTER TYPE</primary>
 </indexterm>

 <refsynopsisdiv>
<synopsis>
ALTER TYPE <replaceable class="PARAMETER">name</replaceable> <replaceable class="PARAMETER">action</replaceable> [, ... ]
ALTER TYPE <replaceable class="PARAMETER">name</replaceable> OWNER TO <replaceable class="PARAMETER">new_owner</replaceable>
ALTER TYPE <replaceable class="PARAMETER">name</replaceable> RENAME ATTRIBUTE <replaceable class="PARAMETER">attribute_name</replaceable> TO <replaceable class="PARAMETER">new_attribute_name</replaceable>
ALTER TYPE <replaceable class="PARAMETER">name</replaceable> RENAME TO <replaceable class="PARAMETER">new_name</replaceable>
ALTER TYPE <replaceable class="PARAMETER">name</replaceable> SET SCHEMA <replaceable class="PARAMETER">new_schema</replaceable>
ALTER TYPE <replaceable class="PARAMETER">name</replaceable> ADD VALUE <replaceable class="PARAMETER">new_enum_value</replaceable> [ { BEFORE | AFTER } <replaceable class="PARAMETER">existing_enum_value</replaceable> ]

<phrase>where <replaceable class="PARAMETER">action</replaceable> is one of:</phrase>

    ADD ATTRIBUTE <replaceable class="PARAMETER">attribute_name</replaceable> <replaceable class="PARAMETER">data_type</replaceable>
    DROP ATTRIBUTE [ IF EXISTS ] <replaceable class="PARAMETER">attribute_name</replaceable>
    ALTER ATTRIBUTE <replaceable class="PARAMETER">attribute_name</replaceable> [ SET DATA ] TYPE <replaceable class="PARAMETER">data_type</replaceable>
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <command>ALTER TYPE</command> changes the definition of an existing type.
   There are several subforms:

  <variablelist>
   <varlistentry>
    <term><literal>ADD ATTRIBUTE</literal></term>
    <listitem>
     <para>
      This form adds a new attribute to a composite type, using the same syntax as
      <xref linkend="SQL-CREATETYPE">.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>DROP ATTRIBUTE [ IF EXISTS ]</literal></term>
    <listitem>
     <para>
      This form drops an attribute from a composite type.
      If <literal>IF EXISTS</literal> is specified and the attribute
      does not exist, no error is thrown. In this case a notice
      is issued instead.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>SET DATA TYPE</literal></term>
    <listitem>
     <para>
      This form changes the type of an attribute of a composite type.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>OWNER</literal></term>
    <listitem>
     <para>
      This form changes the owner of the type.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>RENAME</literal></term>
    <listitem>
     <para>
      This form changes the name of the type or the name of an
      individual attribute of a composite type.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>SET SCHEMA</literal></term>
    <listitem>
     <para>
      This form moves the type into another schema.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>ADD VALUE [ BEFORE | AFTER ]</literal></term>
    <listitem>
     <para>
      This form adds a new value to an enum type. If the new value's place in
      the enum's ordering is not specified using <literal>BEFORE</literal> or
      <literal>AFTER</literal>, then the new item is placed at the end of the
      list of values.
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
  </para>

  <para>
   The <literal>ADD ATTRIBUTE</literal>, <literal>DROP
   ATTRIBUTE</literal>, and <literal>ALTER ATTRIBUTE</literal> actions
   can be combined into a list of multiple alterations to apply in
   parallel.  For example, it is possible to add several attributes
   and/or alter the type of several attributes in a single command.
  </para>

  <para>
   You must own the type to use <command>ALTER TYPE</>.
   To change the schema of a type, you must also have
   <literal>CREATE</literal> privilege on the new schema.
   To alter the owner, you must also be a direct or indirect member of the new
   owning role, and that role must have <literal>CREATE</literal> privilege on
   the type's schema.  (These restrictions enforce that altering the owner
   doesn't do anything you couldn't do by dropping and recreating the type.
   However, a superuser can alter ownership of any type anyway.)
  </para>
 </refsect1>

 <refsect1>
  <title>Parameters</title>

   <para>
    <variablelist>
     <varlistentry>
      <term><replaceable class="PARAMETER">name</replaceable></term>
      <listitem>
       <para>
        The name (possibly schema-qualified) of an existing type to
        alter.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="PARAMETER">new_name</replaceable></term>
      <listitem>
       <para>
        The new name for the type.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="PARAMETER">new_owner</replaceable></term>
      <listitem>
       <para>
        The user name of the new owner of the type.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="PARAMETER">new_schema</replaceable></term>
      <listitem>
       <para>
        The new schema for the type.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="PARAMETER">attribute_name</replaceable></term>
      <listitem>
       <para>
        The name of the attribute to add, alter, or drop.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="PARAMETER">new_attribute_name</replaceable></term>
      <listitem>
       <para>
        The new name of the attribute to be renamed.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="PARAMETER">data_type</replaceable></term>
      <listitem>
       <para>
        The data type of the attribute to add, or the new type of the
        attribute to alter.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="PARAMETER">new_enum_value</replaceable></term>
      <listitem>
       <para>
        The new value to be added to an enum type's list of values.
        Like all enum literals, it needs to be quoted.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="PARAMETER">existing_enum_value</replaceable></term>
      <listitem>
       <para>
        The existing enum value that the new value should be added immediately
        before or after in the enum type's sort ordering.
        Like all enum literals, it needs to be quoted.
       </para>
      </listitem>
     </varlistentry>

    </variablelist>
   </para>
  </refsect1>

 <refsect1>
  <title>Notes</title>

  <para>
   <command>ALTER TYPE ... ADD VALUE</> (the form that adds a new value to an
   enum type) cannot be executed inside a transaction block.
  </para>

  <para>
   Comparisons involving an added enum value will sometimes be slower than
   comparisons involving only original members of the enum type.  This will
   usually only occur if <literal>BEFORE</literal> or <literal>AFTER</literal>
   is used to set the new value's sort position somewhere other than at the
   end of the list.  However, sometimes it will happen even though the new
   value is added at the end (this occurs if the OID counter <quote>wrapped
   around</> since the original creation of the enum type).  The slowdown is
   usually insignificant; but if it matters, optimal performance can be
   regained by dropping and recreating the enum type, or by dumping and
   reloading the database.
  </para>
 </refsect1>

 <refsect1>
  <title>Examples</title>

  <para>
   To rename a data type:
<programlisting>
ALTER TYPE electronic_mail RENAME TO email;
</programlisting>
  </para>

  <para>
   To change the owner of the type <literal>email</literal>
   to <literal>joe</literal>:
<programlisting>
ALTER TYPE email OWNER TO joe;
</programlisting>
  </para>

  <para>
   To change the schema of the type <literal>email</literal>
   to <literal>customers</literal>:
<programlisting>
ALTER TYPE email SET SCHEMA customers;
</programlisting>
  </para>

  <para>
   To add a new attribute to a type:
<programlisting>
ALTER TYPE compfoo ADD ATTRIBUTE f3 int;
</programlisting>
  </para>

  <para>
   To add a new value to an enum type in a particular sort position:
<programlisting>
ALTER TYPE colors ADD VALUE 'orange' AFTER 'red';
</programlisting>
  </para>
 </refsect1>

 <refsect1>
  <title>Compatibility</title>

  <para>
   The variants to add and drop attributes are part of the SQL
   standard; the other variants are PostgreSQL extensions.
  </para>
 </refsect1>

 <refsect1 id="SQL-ALTERTYPE-see-also">
  <title>See Also</title>

  <simplelist type="inline">
   <member><xref linkend="sql-createtype"></member>
   <member><xref linkend="sql-droptype"></member>
  </simplelist>
 </refsect1>
</refentry>
