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<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>
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 STATISTICS <replaceable class="PARAMETER">integer</replaceable>
ALTER TABLE [ ONLY ] <replaceable class="PARAMETER">table</replaceable> [ * ]
    RENAME [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> TO <replaceable
    class="PARAMETER">newcolumn</replaceable>
ALTER TABLE <replaceable class="PARAMETER">table</replaceable>
    RENAME TO <replaceable class="PARAMETER">newtable</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</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 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"> newcolumn </replaceable></term>
      <listitem>
       <para>
	New name for an existing column.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="PARAMETER"> newtable </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">New user </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.
   The <literal>ADD COLUMN</literal> form adds a new column to the table
   using the same syntax as <xref linkend="SQL-CREATETABLE"
   endterm="SQL-CREATETABLE-title">.
   The <literal>ALTER COLUMN SET/DROP DEFAULT</literal> forms
   allow you to set or remove the default for the column. Note that defaults
   only apply to subsequent <command>INSERT</command> commands; they do not
   cause rows already in the table to change.
   The <literal>ALTER COLUMN SET STATISTICS</literal> form allows you to
   set the statistics-gathering target for subsequent
   <xref linkend="sql-analyze" endterm="sql-analyze-title"> operations.
   The <literal>RENAME</literal> clause causes the name of a table or column
   to change without changing any of the data contained in
   the affected table. Thus, the table or column will
   remain of the same type and size after this command is
   executed.
   The ADD <replaceable class="PARAMETER">table constraint definition</replaceable> clause 
   adds a new constraint to the table using the same syntax as <xref
   linkend="SQL-CREATETABLE" endterm="SQL-CREATETABLE-title">. 
   The DROP CONSTRAINT <replaceable class="PARAMETER">constraint</replaceable> clause 
   drops all CHECK constraints on the table (and its children) that match <replaceable class="PARAMETER">constraint</replaceable>.
   The OWNER clause changes the owner of the table to the user <replaceable class="PARAMETER">
   new user</replaceable>.
  </para>

  <para>
   You must own the table in order to change its schema.
  </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 constraint clauses for the
    new column will be ignored. You can use the <literal>SET DEFAULT</literal>
    form of <command>ALTER TABLE</command> to set the default later.
    (You may also want to update the already existing rows to the
    new default value, using <xref linkend="sql-update"
    endterm="sql-update-title">.)
   </para>

   <para>
    In the current implementation, only UNIQUE, FOREIGN KEY and CHECK constraints can
    be added to a table.  To create a primary constraint, create 
    a unique, not null index (see <xref linkend="SQL-CREATEINDEX" 
    endterm="SQL-CREATEINDEX-title">).
   </para>

	<para>
    Currently only CHECK constraints can be dropped from a table.  The RESTRICT
	 keyword is required, although dependencies are not checked.  The CASCADE
	 option is unsupported.  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>
    You must own the table in order to change it.
    Changing any  part  of  the schema of a system
    catalog is not permitted.
    The <citetitle>PostgreSQL User's Guide</citetitle> has further
    information on inheritance.
   </para>

   <para>
    Refer to <command>CREATE TABLE</command> for a further description
    of valid arguments.
   </para>
  </refsect2>
 </refsect1>

 <refsect1 id="R1-SQL-ALTERTABLE-2">
  <title>
   Usage
  </title>
  <para>
   To add a column of type VARCHAR 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 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;
   </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 (multi-column) unique constraint to a table:
   <programlisting>
ALTER TABLE distributors ADD CONSTRAINT dist_id_zipcode_key UNIQUE (dist_id, zipcode);
   </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 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>Postgres</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 columns and tables are <productname>Postgres</productname>
    extensions from SQL92.
   </para>
 
  </refsect2>
 </refsect1>
</refentry>

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