<!--
$Header: /cvsroot/pgsql/doc/src/sgml/ref/alter_table.sgml,v 1.44 2002/04/24 02:40:45 momjian Exp $
PostgreSQL documentation
-->

<refentry id="SQL-ALTERTABLE">
 <refmeta>
  <refentrytitle id="sql-altertable-title">ALTER TABLE</refentrytitle>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>
 <refnamediv>
  <refname>
   ALTER TABLE
  </refname>
  <refpurpose>
   change the definition of a table
  </refpurpose>
 </refnamediv>
 <refsynopsisdiv>
  <refsynopsisdivinfo>
   <date>1999-07-20</date>
  </refsynopsisdivinfo>
  <synopsis>
ALTER TABLE [ ONLY ] <replaceable class="PARAMETER">table</replaceable> [ * ]
    ADD [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> <replaceable class="PARAMETER">type</replaceable> [ <replaceable class="PARAMETER">column_constraint</replaceable> [ ... ] ]
ALTER TABLE [ ONLY ] <replaceable class="PARAMETER">table</replaceable> [ * ]
    ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> { SET DEFAULT <replaceable class="PARAMETER">value</replaceable> | DROP DEFAULT }
ALTER TABLE [ ONLY ] <replaceable class="PARAMETER">table</replaceable> [ * ]
    ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> { SET | DROP } NOT NULL
ALTER TABLE [ ONLY ] <replaceable class="PARAMETER">table</replaceable> [ * ]
    ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> SET STATISTICS <replaceable class="PARAMETER">integer</replaceable>
ALTER TABLE [ ONLY ] <replaceable class="PARAMETER">table</replaceable> [ * ]
    ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> SET STORAGE { PLAIN | EXTERNAL | EXTENDED | MAIN }
ALTER TABLE [ ONLY ] <replaceable class="PARAMETER">table</replaceable> [ * ]
    RENAME [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> TO <replaceable
    class="PARAMETER">new_column</replaceable>
ALTER TABLE <replaceable class="PARAMETER">table</replaceable>
    RENAME TO <replaceable class="PARAMETER">new_table</replaceable>
ALTER TABLE <replaceable class="PARAMETER">table</replaceable>
    ADD <replaceable class="PARAMETER">table_constraint_definition</replaceable>
ALTER TABLE [ ONLY ] <replaceable class="PARAMETER">table</replaceable> 
	DROP CONSTRAINT <replaceable class="PARAMETER">constraint_name</replaceable> { RESTRICT | CASCADE }
ALTER TABLE <replaceable class="PARAMETER">table</replaceable>
	OWNER TO <replaceable class="PARAMETER">new_owner</replaceable> 
  </synopsis>

  <refsect2 id="R2-SQL-ALTERTABLE-1">
   <refsect2info>
    <date>1998-04-15</date>
   </refsect2info>
   <title>
    Inputs
   </title>
   <para>
    <variablelist>

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

     <varlistentry>
      <term><replaceable class="PARAMETER"> column </replaceable></term>
      <listitem>
       <para>
	Name of a new or existing column.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="PARAMETER"> type </replaceable></term>
      <listitem>
       <para>
	Type of the new column.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="PARAMETER"> new_column </replaceable></term>
      <listitem>
       <para>
	New name for an existing column.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="PARAMETER"> new_table </replaceable></term>
      <listitem>
       <para>
	New name for the table.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="PARAMETER"> table_constraint_definition </replaceable></term>
      <listitem>
       <para>
	New table constraint for the table.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="PARAMETER"> constraint_name </replaceable></term>
      <listitem>
       <para>
	Name of an existing constraint to drop.
       </para>
      </listitem>
     </varlistentry>

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

    </variablelist>
   </para>
  </refsect2>

  <refsect2 id="R2-SQL-ALTERTABLE-2">
   <refsect2info>
    <date>1998-04-15</date>
   </refsect2info>
   <title>
    Outputs
   </title>
   <para>

    <variablelist>
     <varlistentry>
      <term><computeroutput>ALTER</computeroutput></term>
      <listitem>
       <para>
	Message returned from column or table renaming.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><computeroutput>ERROR</computeroutput></term>
      <listitem>
       <para>
	Message returned if table or column is not available.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>
  </refsect2>
 </refsynopsisdiv>

 <refsect1 id="R1-SQL-ALTERTABLE-1">
  <refsect1info>
   <date>1998-04-15</date>
  </refsect1info>
  <title>
   Description
  </title>
  <para>
   <command>ALTER TABLE</command> changes the definition of an existing table.
   There are several sub-forms:
  </para>

  <variablelist>

   <varlistentry>
    <term>ADD COLUMN</term>
    <listitem>
     <para>
      This form adds a new column to the table using the same syntax as
      <xref linkend="SQL-CREATETABLE" endterm="SQL-CREATETABLE-TITLE">.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term>SET/DROP DEFAULT</term>
    <listitem>
     <para>
      These forms set or remove the default value for a column. Note
      that defaults only apply to subsequent <command>INSERT</command>
      commands; they do not cause rows already in the table to change.
      Defaults may also be created for views, in which case they are
      inserted into <command>INSERT</> statements on the view before
      the view's ON INSERT rule is applied.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term>SET/DROP NOT NULL</term>
    <listitem>
     <para>
      These forms change whether a column is marked to allow NULL
      values or to reject NULL values.  You may only <literal>SET NOT NULL</>
      when the table contains no NULLs in the column.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term>SET STATISTICS</term>
    <listitem>
     <para>
      This form
      sets the per-column statistics-gathering target for subsequent
      <xref linkend="sql-analyze" endterm="sql-analyze-title"> operations.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term>SET STORAGE</term>
    <listitem>
     <para>
      This form sets the storage mode for a column. This controls whether this
      column is held inline or in a supplementary table, and whether the data
      should be compressed or not. <literal>PLAIN</literal> must be used
      for fixed-length values such as <literal>INTEGER</literal> and is
      inline, uncompressed. <literal>MAIN</literal> is for inline,
      compressible data. <literal>EXTERNAL</literal> is for external,
      uncompressed data and <literal>EXTENDED</literal> is for external,
      compressed data.  <literal>EXTENDED</literal> is the default for all
      datatypes that support it.  The use of <literal>EXTERNAL</literal> will
      make substring operations on a TEXT column faster, at the penalty of
      increased storage space.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term>RENAME</term>
    <listitem>
     <para>
      The <literal>RENAME</literal> forms change the name of  a table
      (or an index, sequence, or view) or the name of an individual column in
      a table. There is no effect on the stored data.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term>ADD <replaceable class="PARAMETER">table_constraint_definition</replaceable></term>
    <listitem>
     <para>
      This form adds a new constraint to a table using the same syntax as
      <xref linkend="SQL-CREATETABLE" endterm="SQL-CREATETABLE-TITLE">. 
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term>DROP CONSTRAINT</term>
    <listitem>
     <para>
      This form drops constraints on a table (and its children).
      Currently, constraints on tables are not required to have unique
      names, so there may be more than one constraint matching the specified
      name.  All such constraints will be dropped.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term>OWNER</term>
    <listitem>
     <para>
      This form changes the owner of the table, index, sequence or view to the
      specified user.
     </para>
    </listitem>
   </varlistentry>

  </variablelist>

  <para>
   You must own the table to use <command>ALTER TABLE</>; except for
   <command>ALTER TABLE OWNER</>, which may only be executed by a superuser.
  </para>

  <refsect2 id="R2-SQL-ALTERTABLE-3">
   <refsect2info>
    <date>1998-04-15</date>
   </refsect2info>
   <title>
    Notes
</title>
   <para>
    The keyword <literal>COLUMN</literal> is noise and can be omitted.
   </para>

   <para>
    In the current implementation of <literal>ADD COLUMN</literal>,
    default and NOT NULL clauses for the new column are not supported.
    The new column always comes into being with all values NULL.
    You can use the <literal>SET DEFAULT</literal> form
    of <command>ALTER TABLE</command> to set the default afterwards.
    (You may also want to update the already existing rows to the
    new default value, using
    <xref linkend="sql-update" endterm="sql-update-title">.)
    If you want to mark the column non-null, use the <literal>SET NOT NULL</>
    form after you've entered non-null values for the column in all rows.
   </para>

   <para>
    In DROP CONSTRAINT, the RESTRICT keyword is required, although
    dependencies are not yet checked.  The CASCADE option is unsupported.  
    Currently DROP CONSTRAINT only handles CHECK constraints.
    To remove a PRIMARY or UNIQUE constraint, drop the 
    relevant index using the <xref linkend="SQL-DROPINDEX" endterm="sql-dropindex-title"> command.
    To remove FOREIGN KEY constraints you need to recreate
    and reload the table, using other parameters to the
    <xref linkend="SQL-CREATETABLE" endterm="sql-createtable-title"> command.
   </para>
   <para>
    For example, to drop all constraints on a table <literal>distributors</literal>:
    <programlisting>
CREATE TABLE temp AS SELECT * FROM distributors;
DROP TABLE distributors;
CREATE TABLE distributors AS SELECT * FROM temp;
DROP TABLE temp;
    </programlisting>
   </para>

   <para>
    Changing any  part  of  the schema of a system
    catalog is not permitted.
   </para>

   <para>
    Refer to <command>CREATE TABLE</command> for a further description
    of valid arguments.
    The <citetitle>PostgreSQL User's Guide</citetitle> has further
    information on inheritance.
   </para>
  </refsect2>
 </refsect1>

 <refsect1 id="R1-SQL-ALTERTABLE-2">
  <title>
   Usage
  </title>
  <para>
   To add a column of type <type>varchar</type> to a table:
   <programlisting>
ALTER TABLE distributors ADD COLUMN address VARCHAR(30);
   </programlisting>
  </para>

  <para>
   To rename an existing column:
   <programlisting>
ALTER TABLE distributors RENAME COLUMN address TO city;
   </programlisting>
  </para>

  <para>
   To rename an existing table:
   <programlisting>
ALTER TABLE distributors RENAME TO suppliers;
   </programlisting>
  </para>

  <para>
   To add a NOT NULL constraint to a column:
   <programlisting>
ALTER TABLE distributors ALTER COLUMN street SET NOT NULL;
   </programlisting>
   To remove a NOT NULL constraint from a column:
   <programlisting>
ALTER TABLE distributors ALTER COLUMN street DROP NOT NULL;
   </programlisting>
  </para>

  <para> 
   To add a check constraint to a table:
   <programlisting>
ALTER TABLE distributors ADD CONSTRAINT zipchk CHECK (char_length(zipcode) = 5);
   </programlisting>
  </para>

  <para> 
   To remove a check constraint from a table and all its children:
   <programlisting>
ALTER TABLE distributors DROP CONSTRAINT zipchk RESTRICT;
   </programlisting>
  </para>

  <para> 
   To add a foreign key constraint to a table:
   <programlisting>
ALTER TABLE distributors ADD CONSTRAINT distfk FOREIGN KEY (address) REFERENCES addresses(address) MATCH FULL;
   </programlisting>
  </para>

  <para> 
   To add a (multicolumn) unique constraint to a table:
   <programlisting>
ALTER TABLE distributors ADD CONSTRAINT dist_id_zipcode_key UNIQUE (dist_id, zipcode);
   </programlisting>
  </para>

  <para> 
   To add an automatically named primary key constraint to a table, noting
   that a table can only ever have one primary key:
   <programlisting>
ALTER TABLE distributors ADD PRIMARY KEY (dist_id);
   </programlisting>
  </para>
 </refsect1>

 <refsect1 id="R1-SQL-ALTERTABLE-3">
  <title>
   Compatibility
  </title>

  <refsect2 id="R2-SQL-ALTERTABLE-4">
   <refsect2info>
    <date>1998-04-15</date>
   </refsect2info>
   <title>SQL92</title>
    <para>
     The <literal>ADD COLUMN</literal> form is compliant with the exception that
     it does not support defaults and NOT NULL constraints, as explained above.
     The <literal>ALTER COLUMN</literal> form is in full compliance.
    </para>

    <para>
     SQL92 specifies some additional capabilities for <command>ALTER TABLE</command>
     statement which are not yet directly supported by <productname>PostgreSQL</productname>:

    <variablelist>
    <varlistentry>
     <term>
      <synopsis>
ALTER TABLE <replaceable class="PARAMETER">table</replaceable> DROP [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> { RESTRICT | CASCADE }
      </synopsis>
     </term>
     <listitem>
      <para>
       Removes a column from a table.
       Currently, to remove an existing column the table must be
       recreated and reloaded:
       <programlisting>
CREATE TABLE temp AS SELECT did, city FROM distributors;    
DROP TABLE distributors;
CREATE TABLE distributors (
    did      DECIMAL(3)  DEFAULT 1,
    name     VARCHAR(40) NOT NULL
);
INSERT INTO distributors SELECT * FROM temp;
DROP TABLE temp;
       </programlisting>
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
   </para>

   <para>
    The clauses to rename tables, columns, indexes, and sequences are
    <productname>PostgreSQL</productname> extensions from SQL92.
   </para>
 
  </refsect2>
 </refsect1>
</refentry>

<!-- Keep this comment at the end of the file
Local variables:
mode: sgml
sgml-omittag:nil
sgml-shorttag:t
sgml-minimize-attributes:nil
sgml-always-quote-attributes:t
sgml-indent-step:1
sgml-indent-data:t
sgml-parent-document:nil
sgml-default-dtd-file:"../reference.ced"
sgml-exposed-tags:nil
sgml-local-catalogs:"/usr/lib/sgml/catalog"
sgml-local-ecat-files:nil
End:
-->
