alter_table.sgml

postgresql8.3.4源码,开源数据库

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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>

 <indexterm zone="sql-altertable">
  <primary>ALTER TABLE</primary>
 </indexterm>

 <refsynopsisdiv>
<synopsis>
ALTER TABLE [ ONLY ] <replaceable class="PARAMETER">name</replaceable> [ * ]
    <replaceable class="PARAMETER">action</replaceable> [, ... ]
ALTER TABLE [ ONLY ] <replaceable class="PARAMETER">name</replaceable> [ * ]
    RENAME [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> TO <replaceable class="PARAMETER">new_column</replaceable>
ALTER TABLE <replaceable class="PARAMETER">name</replaceable>
    RENAME TO <replaceable class="PARAMETER">new_name</replaceable>
ALTER TABLE <replaceable class="PARAMETER">name</replaceable>
    SET SCHEMA <replaceable class="PARAMETER">new_schema</replaceable>

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

    ADD [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> <replaceable class="PARAMETER">type</replaceable> [ <replaceable class="PARAMETER">column_constraint</replaceable> [ ... ] ]
    DROP [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> [ RESTRICT | CASCADE ]
    ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> TYPE <replaceable class="PARAMETER">type</replaceable> [ USING <replaceable class="PARAMETER">expression</replaceable> ]
    ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> SET DEFAULT <replaceable class="PARAMETER">expression</replaceable>
    ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> DROP DEFAULT
    ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> { SET | DROP } NOT NULL
    ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> SET STATISTICS <replaceable class="PARAMETER">integer</replaceable>
    ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> SET STORAGE { PLAIN | EXTERNAL | EXTENDED | MAIN }
    ADD <replaceable class="PARAMETER">table_constraint</replaceable>
    DROP CONSTRAINT <replaceable class="PARAMETER">constraint_name</replaceable> [ RESTRICT | CASCADE ]
    DISABLE TRIGGER [ <replaceable class="PARAMETER">trigger_name</replaceable> | ALL | USER ]
    ENABLE TRIGGER [ <replaceable class="PARAMETER">trigger_name</replaceable> | ALL | USER ]
    ENABLE REPLICA TRIGGER <replaceable class="PARAMETER">trigger_name</replaceable>
    ENABLE ALWAYS TRIGGER <replaceable class="PARAMETER">trigger_name</replaceable>
    DISABLE RULE <replaceable class="PARAMETER">rewrite_rule_name</replaceable>
    ENABLE RULE <replaceable class="PARAMETER">rewrite_rule_name</replaceable>
    ENABLE REPLICA RULE <replaceable class="PARAMETER">rewrite_rule_name</replaceable>
    ENABLE ALWAYS RULE <replaceable class="PARAMETER">rewrite_rule_name</replaceable>
    CLUSTER ON <replaceable class="PARAMETER">index_name</replaceable>
    SET WITHOUT CLUSTER
    SET WITHOUT OIDS
    SET ( <replaceable class="PARAMETER">storage_parameter</replaceable> = <replaceable class="PARAMETER">value</replaceable> [, ... ] )
    RESET ( <replaceable class="PARAMETER">storage_parameter</replaceable> [, ... ] )
    INHERIT <replaceable class="PARAMETER">parent_table</replaceable>
    NO INHERIT <replaceable class="PARAMETER">parent_table</replaceable>
    OWNER TO <replaceable class="PARAMETER">new_owner</replaceable>
    SET TABLESPACE <replaceable class="PARAMETER">new_tablespace</replaceable>
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

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

  <variablelist>
   <varlistentry>
    <term><literal>ADD COLUMN</literal></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><literal>DROP COLUMN</literal></term>
    <listitem>
     <para>
      This form drops a column from a table.  Indexes and
      table constraints involving the column will be automatically
      dropped as well.  You will need to say <literal>CASCADE</> if
      anything outside the table depends on the column, for example,
      foreign key references or views.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>ALTER COLUMN TYPE</literal></term>
    <listitem>
     <para>
      This form changes the type of a column of a table. Indexes and
      simple table constraints involving the column will be automatically
      converted to use the new column type by reparsing the originally
      supplied expression.  The optional <literal>USING</literal>
      clause specifies how to compute the new column value from the old;
      if omitted, the default conversion is the same as an assignment
      cast from old data type to new.  A  <literal>USING</literal>
      clause must be provided if there is no implicit or assignment
      cast from old to new type.
     </para>
    </listitem>
   </varlistentry>

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

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

   <varlistentry>
    <term><literal>SET STATISTICS</literal></term>
    <listitem>
     <para>
      This form
      sets the per-column statistics-gathering target for subsequent
      <xref linkend="sql-analyze" endterm="sql-analyze-title"> operations.
      The target can be set in the range 0 to 1000; alternatively, set it
      to -1 to revert to using the system default statistics
      target (<xref linkend="guc-default-statistics-target">).
      For more information on the use of statistics by the
      <productname>PostgreSQL</productname> query planner, refer to
      <xref linkend="planner-stats">.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <indexterm>
     <primary>TOAST</primary>
     <secondary>per-column storage settings</secondary>
    </indexterm>

    <term><literal>SET STORAGE</literal></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 <type>integer</type> 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 most
      data types that support non-<literal>PLAIN</literal> storage.
      Use of <literal>EXTERNAL</literal> will
      make substring operations on <type>text</type> and <type>bytea</type>
      columns faster, at the penalty of increased storage space.  Note that
      <literal>SET STORAGE</> doesn't itself change anything in the table,
      it just sets the strategy to be pursued during future table updates.
      See <xref linkend="storage-toast"> for more information.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>ADD <replaceable class="PARAMETER">table_constraint</replaceable></literal></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><literal>DROP CONSTRAINT</literal></term>
    <listitem>
     <para>
      This form drops the specified constraint on a table.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>DISABLE</literal>/<literal>ENABLE [ REPLICA | ALWAYS ] TRIGGER</literal></term>
    <listitem>
     <para>
      These forms configure the firing of trigger(s) belonging to the table.
      A disabled trigger is still known to the system, but is not executed
      when its triggering event occurs.  For a deferred trigger, the enable
      status is checked when the event occurs, not when the trigger function
      is actually executed.  One can disable or enable a single
      trigger specified by name, or all triggers on the table, or only
      user triggers (this option excludes triggers that are used to implement
      foreign key constraints).  Disabling or enabling constraint triggers
      requires superuser privileges; it should be done with caution since
      of course the integrity of the constraint cannot be guaranteed if the
      triggers are not executed.
      The trigger firing mechanism is also affected by the configuration
      variable <xref linkend="guc-session-replication-role">. Simply enabled
      triggers will fire when the replication role is <quote>origin</>
      (the default) or <quote>local</>. Triggers configured <literal>ENABLE REPLICA</literal>
      will only fire if the session is in <quote>replica</> mode and triggers 
      configured <literal>ENABLE ALWAYS</literal> will fire regardless of the current replication 
      mode.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>DISABLE</literal>/<literal>ENABLE [ REPLICA | ALWAYS ] RULE</literal></term>
    <listitem>
     <para>
      These forms configure the firing of rewrite rules belonging to the table.
      A disabled rule is still known to the system, but is not applied
      during query rewriting. The semantics are as for disabled/enabled
      triggers. This configuration is ignored for <literal>ON SELECT</literal> rules, which
      are always applied in order to keep views working even if the current
      session is in a non-default replication role.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>CLUSTER</literal></term>
    <listitem>
     <para>
      This form selects the default index for future 
      <xref linkend="SQL-CLUSTER" endterm="sql-cluster-title">
      operations.  It does not actually re-cluster the table.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>SET WITHOUT CLUSTER</literal></term>
    <listitem>
     <para>
      This form removes the most recently used
      <xref linkend="SQL-CLUSTER" endterm="sql-cluster-title">
      index specification from the table.  This affects
      future cluster operations that don't specify an index.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>SET WITHOUT OIDS</literal></term>
    <listitem>
     <para>
      This form removes the <literal>oid</literal> system column from the
      table.  This is exactly equivalent to
      <literal>DROP COLUMN oid RESTRICT</literal>,
      except that it will not complain if there is already no
      <literal>oid</literal> column.
     </para>

     <para>
      Note that there is no variant of <command>ALTER TABLE</command>
      that allows OIDs to be restored to a table once they have been
      removed.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>SET ( <replaceable class="PARAMETER">storage_parameter</replaceable> = <replaceable class="PARAMETER">value</replaceable> [, ... ] )</literal></term>
    <listitem>
     <para>
      This form changes one or more storage parameters for the table.  See
      <xref linkend="SQL-CREATETABLE" endterm="sql-createtable-title">
      for details on the available parameters.  Note that the table contents
      will not be modified immediately by this command; depending on the
      parameter you might need to rewrite the table to get the desired effects.
      That can be done with <xref linkend="SQL-CLUSTER"