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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>ALTER INDEX</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="sql-altergroup.html" title="ALTER GROUP" /><link rel="next" href="sql-alterlanguage.html" title="ALTER LANGUAGE" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">ALTER INDEX</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="sql-altergroup.html" title="ALTER GROUP">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="sql-commands.html" title="SQL Commands">Up</a></td><th width="60%" align="center">SQL Commands</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 11.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="sql-alterlanguage.html" title="ALTER LANGUAGE">Next</a></td></tr></table><hr></hr></div><div class="refentry" id="SQL-ALTERINDEX"><div class="titlepage"></div><a id="id-1.9.3.16.1" class="indexterm"></a><div class="refnamediv"><h2><span class="refentrytitle">ALTER INDEX</span></h2><p>ALTER INDEX — change the definition of an index</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><pre class="synopsis">
ALTER INDEX [ IF EXISTS ] <em class="replaceable"><code>name</code></em> RENAME TO <em class="replaceable"><code>new_name</code></em>
ALTER INDEX [ IF EXISTS ] <em class="replaceable"><code>name</code></em> SET TABLESPACE <em class="replaceable"><code>tablespace_name</code></em>
ALTER INDEX <em class="replaceable"><code>name</code></em> ATTACH PARTITION <em class="replaceable"><code>index_name</code></em>
ALTER INDEX <em class="replaceable"><code>name</code></em> DEPENDS ON EXTENSION <em class="replaceable"><code>extension_name</code></em>
ALTER INDEX [ IF EXISTS ] <em class="replaceable"><code>name</code></em> SET ( <em class="replaceable"><code>storage_parameter</code></em> = <em class="replaceable"><code>value</code></em> [, ... ] )
ALTER INDEX [ IF EXISTS ] <em class="replaceable"><code>name</code></em> RESET ( <em class="replaceable"><code>storage_parameter</code></em> [, ... ] )
ALTER INDEX [ IF EXISTS ] <em class="replaceable"><code>name</code></em> ALTER [ COLUMN ] <em class="replaceable"><code>column_number</code></em>
SET STATISTICS <em class="replaceable"><code>integer</code></em>
ALTER INDEX ALL IN TABLESPACE <em class="replaceable"><code>name</code></em> [ OWNED BY <em class="replaceable"><code>role_name</code></em> [, ... ] ]
SET TABLESPACE <em class="replaceable"><code>new_tablespace</code></em> [ NOWAIT ]
</pre></div><div class="refsect1" id="id-1.9.3.16.5"><h2>Description</h2><p>
<code class="command">ALTER INDEX</code> changes the definition of an existing index.
There are several subforms:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="literal">RENAME</code></span></dt><dd><p>
The <code class="literal">RENAME</code> form changes the name of the index.
If the index is associated with a table constraint (either
<code class="literal">UNIQUE</code>, <code class="literal">PRIMARY KEY</code>,
or <code class="literal">EXCLUDE</code>), the constraint is renamed as well.
There is no effect on the stored data.
</p></dd><dt><span class="term"><code class="literal">SET TABLESPACE</code></span></dt><dd><p>
This form changes the index's tablespace to the specified tablespace and
moves the data file(s) associated with the index to the new tablespace.
To change the tablespace of an index, you must own the index and have
<code class="literal">CREATE</code> privilege on the new tablespace.
All indexes in the current database in a tablespace can be moved by using
the <code class="literal">ALL IN TABLESPACE</code> form, which will lock all
indexes to be moved and then move each one. This form also supports
<code class="literal">OWNED BY</code>, which will only move indexes owned by the
roles specified. If the <code class="literal">NOWAIT</code> option is specified
then the command will fail if it is unable to acquire all of the locks
required immediately. Note that system catalogs will not be moved by
this command, use <code class="command">ALTER DATABASE</code> or explicit
<code class="command">ALTER INDEX</code> invocations instead if desired.
See also
<a class="xref" href="sql-createtablespace.html" title="CREATE TABLESPACE"><span class="refentrytitle">CREATE TABLESPACE</span></a>.
</p></dd><dt><span class="term"><code class="literal">ATTACH PARTITION</code></span></dt><dd><p>
Causes the named index to become attached to the altered index.
The named index must be on a partition of the table containing the
index being altered, and have an equivalent definition. An attached
index cannot be dropped by itself, and will automatically be dropped
if its parent index is dropped.
</p></dd><dt><span class="term"><code class="literal">DEPENDS ON EXTENSION</code></span></dt><dd><p>
This form marks the index as dependent on the extension, such that if the
extension is dropped, the index will automatically be dropped as well.
</p></dd><dt><span class="term"><code class="literal">SET ( <em class="replaceable"><code>storage_parameter</code></em> = <em class="replaceable"><code>value</code></em> [, ... ] )</code></span></dt><dd><p>
This form changes one or more index-method-specific storage parameters
for the index. See
<a class="xref" href="sql-createindex.html" title="CREATE INDEX"><span class="refentrytitle">CREATE INDEX</span></a>
for details on the available parameters. Note that the index contents
will not be modified immediately by this command; depending on the
parameter you might need to rebuild the index with
<a class="xref" href="sql-reindex.html" title="REINDEX"><span class="refentrytitle">REINDEX</span></a>
to get the desired effects.
</p></dd><dt><span class="term"><code class="literal">RESET ( <em class="replaceable"><code>storage_parameter</code></em> [, ... ] )</code></span></dt><dd><p>
This form resets one or more index-method-specific storage parameters to
their defaults. As with <code class="literal">SET</code>, a <code class="literal">REINDEX</code>
might be needed to update the index entirely.
</p></dd><dt><span class="term"><code class="literal">ALTER [ COLUMN ] <em class="replaceable"><code>column_number</code></em> SET STATISTICS <em class="replaceable"><code>integer</code></em></code></span></dt><dd><p>
This form sets the per-column statistics-gathering target for
subsequent <a class="xref" href="sql-analyze.html" title="ANALYZE"><span class="refentrytitle">ANALYZE</span></a> operations, though can
be used only on index columns that are defined as an expression.
Since expressions lack a unique name, we refer to them using the
ordinal number of the index column.
The target can be set in the range 0 to 10000; alternatively, set it
to -1 to revert to using the system default statistics
target (<a class="xref" href="runtime-config-query.html#GUC-DEFAULT-STATISTICS-TARGET">default_statistics_target</a>).
For more information on the use of statistics by the
<span class="productname">PostgreSQL</span> query planner, refer to
<a class="xref" href="planner-stats.html" title="14.2. Statistics Used by the Planner">Section 14.2</a>.
</p></dd></dl></div><p>
</p></div><div class="refsect1" id="id-1.9.3.16.6"><h2>Parameters</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="literal">IF EXISTS</code></span></dt><dd><p>
Do not throw an error if the index does not exist. A notice is issued
in this case.
</p></dd><dt><span class="term"><em class="replaceable"><code>column_number</code></em></span></dt><dd><p>
The ordinal number refers to the ordinal (left-to-right) position
of the index column.
</p></dd><dt><span class="term"><em class="replaceable"><code>name</code></em></span></dt><dd><p>
The name (possibly schema-qualified) of an existing index to
alter.
</p></dd><dt><span class="term"><em class="replaceable"><code>new_name</code></em></span></dt><dd><p>
The new name for the index.
</p></dd><dt><span class="term"><em class="replaceable"><code>tablespace_name</code></em></span></dt><dd><p>
The tablespace to which the index will be moved.
</p></dd><dt><span class="term"><em class="replaceable"><code>extension_name</code></em></span></dt><dd><p>
The name of the extension that the index is to depend on.
</p></dd><dt><span class="term"><em class="replaceable"><code>storage_parameter</code></em></span></dt><dd><p>
The name of an index-method-specific storage parameter.
</p></dd><dt><span class="term"><em class="replaceable"><code>value</code></em></span></dt><dd><p>
The new value for an index-method-specific storage parameter.
This might be a number or a word depending on the parameter.
</p></dd></dl></div></div><div class="refsect1" id="id-1.9.3.16.7"><h2>Notes</h2><p>
These operations are also possible using
<a class="xref" href="sql-altertable.html" title="ALTER TABLE"><span class="refentrytitle">ALTER TABLE</span></a>.
<code class="command">ALTER INDEX</code> is in fact just an alias for the forms
of <code class="command">ALTER TABLE</code> that apply to indexes.
</p><p>
There was formerly an <code class="command">ALTER INDEX OWNER</code> variant, but
this is now ignored (with a warning). An index cannot have an owner
different from its table's owner. Changing the table's owner
automatically changes the index as well.
</p><p>
Changing any part of a system catalog index is not permitted.
</p></div><div class="refsect1" id="id-1.9.3.16.8"><h2>Examples</h2><p>
To rename an existing index:
</p><pre class="programlisting">
ALTER INDEX distributors RENAME TO suppliers;
</pre><p>
</p><p>
To move an index to a different tablespace:
</p><pre class="programlisting">
ALTER INDEX distributors SET TABLESPACE fasttablespace;
</pre><p>
</p><p>
To change an index's fill factor (assuming that the index method
supports it):
</p><pre class="programlisting">
ALTER INDEX distributors SET (fillfactor = 75);
REINDEX INDEX distributors;
</pre><p>
Set the statistics-gathering target for an expression index:
</p><pre class="programlisting">
CREATE INDEX coord_idx ON measured (x, y, (z + t));
ALTER INDEX coord_idx ALTER COLUMN 3 SET STATISTICS 1000;
</pre></div><div class="refsect1" id="id-1.9.3.16.9"><h2>Compatibility</h2><p>
<code class="command">ALTER INDEX</code> is a <span class="productname">PostgreSQL</span>
extension.
</p></div><div class="refsect1" id="id-1.9.3.16.10"><h2>See Also</h2><span class="simplelist"><a class="xref" href="sql-createindex.html" title="CREATE INDEX"><span class="refentrytitle">CREATE INDEX</span></a>, <a class="xref" href="sql-reindex.html" title="REINDEX"><span class="refentrytitle">REINDEX</span></a></span></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="sql-altergroup.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="sql-commands.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="sql-alterlanguage.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">ALTER GROUP </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> ALTER LANGUAGE</td></tr></table></div></body></html>
