| Server IP : 103.119.228.120 / Your IP : 3.128.200.165 Web Server : Apache System : Linux v8.techscape8.com 3.10.0-1160.119.1.el7.tuxcare.els2.x86_64 #1 SMP Mon Jul 15 12:09:18 UTC 2024 x86_64 User : nobody ( 99) PHP Version : 5.6.40 Disable Function : shell_exec,symlink,system,exec,proc_get_status,proc_nice,proc_terminate,define_syslog_variables,syslog,openlog,closelog,escapeshellcmd,passthru,ocinum cols,ini_alter,leak,listen,chgrp,apache_note,apache_setenv,debugger_on,debugger_off,ftp_exec,dl,dll,myshellexec,proc_open,socket_bind,proc_close,escapeshellarg,parse_ini_filepopen,fpassthru,exec,passthru,escapeshellarg,escapeshellcmd,proc_close,proc_open,ini_alter,popen,show_source,proc_nice,proc_terminate,proc_get_status,proc_close,pfsockopen,leak,apache_child_terminate,posix_kill,posix_mkfifo,posix_setpgid,posix_setsid,posix_setuid,dl,symlink,shell_exec,system,dl,passthru,escapeshellarg,escapeshellcmd,myshellexec,c99_buff_prepare,c99_sess_put,fpassthru,getdisfunc,fx29exec,fx29exec2,is_windows,disp_freespace,fx29sh_getupdate,fx29_buff_prepare,fx29_sess_put,fx29shexit,fx29fsearch,fx29ftpbrutecheck,fx29sh_tools,fx29sh_about,milw0rm,imagez,sh_name,myshellexec,checkproxyhost,dosyayicek,c99_buff_prepare,c99_sess_put,c99getsource,c99sh_getupdate,c99fsearch,c99shexit,view_perms,posix_getpwuid,posix_getgrgid,posix_kill,parse_perms,parsesort,view_perms_color,set_encoder_input,ls_setcheckboxall,ls_reverse_all,rsg_read,rsg_glob,selfURL,dispsecinfo,unix2DosTime,addFile,system,get_users,view_size,DirFiles,DirFilesWide,DirPrintHTMLHeaders,GetFilesTotal,GetTitles,GetTimeTotal,GetMatchesCount,GetFileMatchesCount,GetResultFiles,fs_copy_dir,fs_copy_obj,fs_move_dir,fs_move_obj,fs_rmdir,SearchText,getmicrotime MySQL : ON | cURL : ON | WGET : ON | Perl : ON | Python : ON | Sudo : ON | Pkexec : ON Directory : /usr/share/doc/postgresql-9.2.24/html/ |
Upload File : |
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<HTML
><HEAD
><TITLE
>CREATE INDEX</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK
REV="MADE"
HREF="mailto:pgsql-docs@postgresql.org"><LINK
REL="HOME"
TITLE="PostgreSQL 9.2.24 Documentation"
HREF="index.html"><LINK
REL="UP"
TITLE="SQL Commands"
HREF="sql-commands.html"><LINK
REL="PREVIOUS"
TITLE="CREATE GROUP"
HREF="sql-creategroup.html"><LINK
REL="NEXT"
TITLE="CREATE LANGUAGE"
HREF="sql-createlanguage.html"><LINK
REL="STYLESHEET"
TYPE="text/css"
HREF="stylesheet.css"><META
HTTP-EQUIV="Content-Type"
CONTENT="text/html; charset=ISO-8859-1"><META
NAME="creation"
CONTENT="2017-11-06T22:43:11"></HEAD
><BODY
CLASS="REFENTRY"
><DIV
CLASS="NAVHEADER"
><TABLE
SUMMARY="Header navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="5"
ALIGN="center"
VALIGN="bottom"
><A
HREF="index.html"
>PostgreSQL 9.2.24 Documentation</A
></TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="top"
><A
TITLE="CREATE GROUP"
HREF="sql-creategroup.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="top"
><A
HREF="sql-commands.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="60%"
ALIGN="center"
VALIGN="bottom"
></TD
><TD
WIDTH="20%"
ALIGN="right"
VALIGN="top"
><A
TITLE="CREATE LANGUAGE"
HREF="sql-createlanguage.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><H1
><A
NAME="SQL-CREATEINDEX"
></A
>CREATE INDEX</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN68879"
></A
><H2
>Name</H2
>CREATE INDEX -- define a new index</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN68884"
></A
><H2
>Synopsis</H2
><PRE
CLASS="SYNOPSIS"
>CREATE [ UNIQUE ] INDEX [ CONCURRENTLY ] [ <TT
CLASS="REPLACEABLE"
><I
>name</I
></TT
> ] ON <TT
CLASS="REPLACEABLE"
><I
>table_name</I
></TT
> [ USING <TT
CLASS="REPLACEABLE"
><I
>method</I
></TT
> ]
( { <TT
CLASS="REPLACEABLE"
><I
>column_name</I
></TT
> | ( <TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> ) } [ COLLATE <TT
CLASS="REPLACEABLE"
><I
>collation</I
></TT
> ] [ <TT
CLASS="REPLACEABLE"
><I
>opclass</I
></TT
> ] [ ASC | DESC ] [ NULLS { FIRST | LAST } ] [, ...] )
[ WITH ( <TT
CLASS="REPLACEABLE"
><I
>storage_parameter</I
></TT
> = <TT
CLASS="REPLACEABLE"
><I
>value</I
></TT
> [, ... ] ) ]
[ TABLESPACE <TT
CLASS="REPLACEABLE"
><I
>tablespace_name</I
></TT
> ]
[ WHERE <TT
CLASS="REPLACEABLE"
><I
>predicate</I
></TT
> ]</PRE
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN68897"
></A
><H2
>Description</H2
><P
> <TT
CLASS="COMMAND"
>CREATE INDEX</TT
> constructs an index
on the specified column(s) of the specified table.
Indexes are primarily used to enhance database performance (though
inappropriate use can result in slower performance).
</P
><P
> The key field(s) for the index are specified as column names,
or alternatively as expressions written in parentheses.
Multiple fields can be specified if the index method supports
multicolumn indexes.
</P
><P
> An index field can be an expression computed from the values of
one or more columns of the table row. This feature can be used
to obtain fast access to data based on some transformation of
the basic data. For example, an index computed on
<TT
CLASS="LITERAL"
>upper(col)</TT
> would allow the clause
<TT
CLASS="LITERAL"
>WHERE upper(col) = 'JIM'</TT
> to use an index.
</P
><P
> <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> provides the index methods
B-tree, hash, GiST, SP-GiST, and GIN. Users can also define their own index
methods, but that is fairly complicated.
</P
><P
> When the <TT
CLASS="LITERAL"
>WHERE</TT
> clause is present, a
<I
CLASS="FIRSTTERM"
>partial index</I
> is created.
A partial index is an index that contains entries for only a portion of
a table, usually a portion that is more useful for indexing than the
rest of the table. For example, if you have a table that contains both
billed and unbilled orders where the unbilled orders take up a small
fraction of the total table and yet that is an often used section, you
can improve performance by creating an index on just that portion.
Another possible application is to use <TT
CLASS="LITERAL"
>WHERE</TT
> with
<TT
CLASS="LITERAL"
>UNIQUE</TT
> to enforce uniqueness over a subset of a
table. See <A
HREF="indexes-partial.html"
>Section 11.8</A
> for more discussion.
</P
><P
> The expression used in the <TT
CLASS="LITERAL"
>WHERE</TT
> clause can refer
only to columns of the underlying table, but it can use all columns,
not just the ones being indexed. Presently, subqueries and
aggregate expressions are also forbidden in <TT
CLASS="LITERAL"
>WHERE</TT
>.
The same restrictions apply to index fields that are expressions.
</P
><P
> All functions and operators used in an index definition must be
<SPAN
CLASS="QUOTE"
>"immutable"</SPAN
>, that is, their results must depend only on
their arguments and never on any outside influence (such as
the contents of another table or the current time). This restriction
ensures that the behavior of the index is well-defined. To use a
user-defined function in an index expression or <TT
CLASS="LITERAL"
>WHERE</TT
>
clause, remember to mark the function immutable when you create it.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN68919"
></A
><H2
>Parameters</H2
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
>UNIQUE</TT
></DT
><DD
><P
> Causes the system to check for
duplicate values in the table when the index is created (if data
already exist) and each time data is added. Attempts to
insert or update data which would result in duplicate entries
will generate an error.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>CONCURRENTLY</TT
></DT
><DD
><P
> When this option is used, <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> will build the
index without taking any locks that prevent concurrent inserts,
updates, or deletes on the table; whereas a standard index build
locks out writes (but not reads) on the table until it's done.
There are several caveats to be aware of when using this option
— see <A
HREF="sql-createindex.html#SQL-CREATEINDEX-CONCURRENTLY"
><I
>Building Indexes Concurrently</I
></A
>.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>name</I
></TT
></DT
><DD
><P
> The name of the index to be created. No schema name can be included
here; the index is always created in the same schema as its parent
table. If the name is omitted, <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> chooses a
suitable name based on the parent table's name and the indexed column
name(s).
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>table_name</I
></TT
></DT
><DD
><P
> The name (possibly schema-qualified) of the table to be indexed.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>method</I
></TT
></DT
><DD
><P
> The name of the index method to be used. Choices are
<TT
CLASS="LITERAL"
>btree</TT
>, <TT
CLASS="LITERAL"
>hash</TT
>,
<TT
CLASS="LITERAL"
>gist</TT
>, <TT
CLASS="LITERAL"
>spgist</TT
> and <TT
CLASS="LITERAL"
>gin</TT
>.
The default method is <TT
CLASS="LITERAL"
>btree</TT
>.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>column_name</I
></TT
></DT
><DD
><P
> The name of a column of the table.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
></DT
><DD
><P
> An expression based on one or more columns of the table. The
expression usually must be written with surrounding parentheses,
as shown in the syntax. However, the parentheses can be omitted
if the expression has the form of a function call.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>collation</I
></TT
></DT
><DD
><P
> The name of the collation to use for the index. By default,
the index uses the collation declared for the column to be
indexed or the result collation of the expression to be
indexed. Indexes with non-default collations can be useful for
queries that involve expressions using non-default collations.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>opclass</I
></TT
></DT
><DD
><P
> The name of an operator class. See below for details.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>ASC</TT
></DT
><DD
><P
> Specifies ascending sort order (which is the default).
</P
></DD
><DT
><TT
CLASS="LITERAL"
>DESC</TT
></DT
><DD
><P
> Specifies descending sort order.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>NULLS FIRST</TT
></DT
><DD
><P
> Specifies that nulls sort before non-nulls. This is the default
when <TT
CLASS="LITERAL"
>DESC</TT
> is specified.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>NULLS LAST</TT
></DT
><DD
><P
> Specifies that nulls sort after non-nulls. This is the default
when <TT
CLASS="LITERAL"
>DESC</TT
> is not specified.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>storage_parameter</I
></TT
></DT
><DD
><P
> The name of an index-method-specific storage parameter. See
<A
HREF="sql-createindex.html#SQL-CREATEINDEX-STORAGE-PARAMETERS"
><I
>Index Storage Parameters</I
></A
>
for details.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>tablespace_name</I
></TT
></DT
><DD
><P
> The tablespace in which to create the index. If not specified,
<A
HREF="runtime-config-client.html#GUC-DEFAULT-TABLESPACE"
>default_tablespace</A
> is consulted, or
<A
HREF="runtime-config-client.html#GUC-TEMP-TABLESPACES"
>temp_tablespaces</A
> for indexes on temporary
tables.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>predicate</I
></TT
></DT
><DD
><P
> The constraint expression for a partial index.
</P
></DD
></DL
></DIV
><DIV
CLASS="REFSECT2"
><A
NAME="SQL-CREATEINDEX-STORAGE-PARAMETERS"
></A
><H3
>Index Storage Parameters</H3
><P
> The optional <TT
CLASS="LITERAL"
>WITH</TT
> clause specifies <I
CLASS="FIRSTTERM"
>storage
parameters</I
> for the index. Each index method has its own set of allowed
storage parameters. The B-tree, hash, GiST and SP-GiST index methods all
accept this parameter:
</P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
>FILLFACTOR</TT
></DT
><DD
><P
> The fillfactor for an index is a percentage that determines how full
the index method will try to pack index pages. For B-trees, leaf pages
are filled to this percentage during initial index build, and also
when extending the index at the right (adding new largest key values).
If pages
subsequently become completely full, they will be split, leading to
gradual degradation in the index's efficiency. B-trees use a default
fillfactor of 90, but any integer value from 10 to 100 can be selected.
If the table is static then fillfactor 100 is best to minimize the
index's physical size, but for heavily updated tables a smaller
fillfactor is better to minimize the need for page splits. The
other index methods use fillfactor in different but roughly analogous
ways; the default fillfactor varies between methods.
</P
></DD
></DL
></DIV
><P
> GiST indexes additionally accept this parameter:
</P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
>BUFFERING</TT
></DT
><DD
><P
> Determines whether the buffering build technique described in
<A
HREF="gist-implementation.html#GIST-BUFFERING-BUILD"
>Section 53.3.1</A
> is used to build the index. With
<TT
CLASS="LITERAL"
>OFF</TT
> it is disabled, with <TT
CLASS="LITERAL"
>ON</TT
> it is enabled, and
with <TT
CLASS="LITERAL"
>AUTO</TT
> it is initially disabled, but turned on
on-the-fly once the index size reaches <A
HREF="runtime-config-query.html#GUC-EFFECTIVE-CACHE-SIZE"
>effective_cache_size</A
>. The default is <TT
CLASS="LITERAL"
>AUTO</TT
>.
</P
></DD
></DL
></DIV
><P
> GIN indexes accept a different parameter:
</P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
>FASTUPDATE</TT
></DT
><DD
><P
> This setting controls usage of the fast update technique described in
<A
HREF="gin-implementation.html#GIN-FAST-UPDATE"
>Section 55.3.1</A
>. It is a Boolean parameter:
<TT
CLASS="LITERAL"
>ON</TT
> enables fast update, <TT
CLASS="LITERAL"
>OFF</TT
> disables it.
(Alternative spellings of <TT
CLASS="LITERAL"
>ON</TT
> and <TT
CLASS="LITERAL"
>OFF</TT
> are
allowed as described in <A
HREF="config-setting.html"
>Section 18.1</A
>.) The
default is <TT
CLASS="LITERAL"
>ON</TT
>.
</P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
> Turning <TT
CLASS="LITERAL"
>FASTUPDATE</TT
> off via <TT
CLASS="COMMAND"
>ALTER INDEX</TT
> prevents
future insertions from going into the list of pending index entries,
but does not in itself flush previous entries. You might want to
<TT
CLASS="COMMAND"
>VACUUM</TT
> the table afterward to ensure the pending list is
emptied.
</P
></BLOCKQUOTE
></DIV
></DD
></DL
></DIV
></DIV
><DIV
CLASS="REFSECT2"
><A
NAME="SQL-CREATEINDEX-CONCURRENTLY"
></A
><H3
>Building Indexes Concurrently</H3
><P
> Creating an index can interfere with regular operation of a database.
Normally <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> locks the table to be indexed against
writes and performs the entire index build with a single scan of the
table. Other transactions can still read the table, but if they try to
insert, update, or delete rows in the table they will block until the
index build is finished. This could have a severe effect if the system is
a live production database. Very large tables can take many hours to be
indexed, and even for smaller tables, an index build can lock out writers
for periods that are unacceptably long for a production system.
</P
><P
> <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> supports building indexes without locking
out writes. This method is invoked by specifying the
<TT
CLASS="LITERAL"
>CONCURRENTLY</TT
> option of <TT
CLASS="COMMAND"
>CREATE INDEX</TT
>.
When this option is used,
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> must perform two scans of the table, and in
addition it must wait for all existing transactions that could potentially
modify or use the index to terminate. Thus
this method requires more total work than a standard index build and takes
significantly longer to complete. However, since it allows normal
operations to continue while the index is built, this method is useful for
adding new indexes in a production environment. Of course, the extra CPU
and I/O load imposed by the index creation might slow other operations.
</P
><P
> In a concurrent index build, the index is actually entered into
the system catalogs in one transaction, then two table scans occur in
two more transactions. Before each table scan, the index build must
wait for existing transactions that have modified the table to terminate.
After the second scan, the index build must wait for any transactions
that have a snapshot (see <A
HREF="mvcc.html"
>Chapter 13</A
>) predating the second
scan to terminate. Then finally the index can be marked ready for use,
and the <TT
CLASS="COMMAND"
>CREATE INDEX</TT
> command terminates.
Even then, however, the index may not be immediately usable for queries:
in the worst case, it cannot be used as long as transactions exist that
predate the start of the index build.
</P
><P
> If a problem arises while scanning the table, such as a
uniqueness violation in a unique index, the <TT
CLASS="COMMAND"
>CREATE INDEX</TT
>
command will fail but leave behind an <SPAN
CLASS="QUOTE"
>"invalid"</SPAN
> index. This index
will be ignored for querying purposes because it might be incomplete;
however it will still consume update overhead. The <SPAN
CLASS="APPLICATION"
>psql</SPAN
>
<TT
CLASS="COMMAND"
>\d</TT
> command will report such an index as <TT
CLASS="LITERAL"
>INVALID</TT
>:
</P><PRE
CLASS="PROGRAMLISTING"
>postgres=# \d tab
Table "public.tab"
Column | Type | Modifiers
--------+---------+-----------
col | integer |
Indexes:
"idx" btree (col) INVALID</PRE
><P>
The recommended recovery
method in such cases is to drop the index and try again to perform
<TT
CLASS="COMMAND"
>CREATE INDEX CONCURRENTLY</TT
>. (Another possibility is to rebuild
the index with <TT
CLASS="COMMAND"
>REINDEX</TT
>. However, since <TT
CLASS="COMMAND"
>REINDEX</TT
>
does not support concurrent builds, this option is unlikely to seem
attractive.)
</P
><P
> Another caveat when building a unique index concurrently is that the
uniqueness constraint is already being enforced against other transactions
when the second table scan begins. This means that constraint violations
could be reported in other queries prior to the index becoming available
for use, or even in cases where the index build eventually fails. Also,
if a failure does occur in the second scan, the <SPAN
CLASS="QUOTE"
>"invalid"</SPAN
> index
continues to enforce its uniqueness constraint afterwards.
</P
><P
> Concurrent builds of expression indexes and partial indexes are supported.
Errors occurring in the evaluation of these expressions could cause
behavior similar to that described above for unique constraint violations.
</P
><P
> Regular index builds permit other regular index builds on the
same table to occur in parallel, but only one concurrent index build
can occur on a table at a time. In both cases, no other types of schema
modification on the table are allowed meanwhile. Another difference
is that a regular <TT
CLASS="COMMAND"
>CREATE INDEX</TT
> command can be performed within
a transaction block, but <TT
CLASS="COMMAND"
>CREATE INDEX CONCURRENTLY</TT
> cannot.
</P
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN69090"
></A
><H2
>Notes</H2
><P
> See <A
HREF="indexes.html"
>Chapter 11</A
> for information about when indexes can
be used, when they are not used, and in which particular situations
they can be useful.
</P
><DIV
CLASS="CAUTION"
><P
></P
><TABLE
CLASS="CAUTION"
BORDER="1"
WIDTH="100%"
><TR
><TD
ALIGN="CENTER"
><B
>Caution</B
></TD
></TR
><TR
><TD
ALIGN="LEFT"
><P
> Hash index operations are not presently WAL-logged,
so hash indexes might need to be rebuilt with <TT
CLASS="COMMAND"
>REINDEX</TT
>
after a database crash if there were unwritten changes.
Also, changes to hash indexes are not replicated over streaming or
file-based replication after the initial base backup, so they
give wrong answers to queries that subsequently use them.
For these reasons, hash index use is presently discouraged.
</P
></TD
></TR
></TABLE
></DIV
><P
> Currently, only the B-tree, GiST and GIN index methods support
multicolumn indexes. Up to 32 fields can be specified by default.
(This limit can be altered when building
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>.) Only B-tree currently
supports unique indexes.
</P
><P
> An <I
CLASS="FIRSTTERM"
>operator class</I
> can be specified for each
column of an index. The operator class identifies the operators to be
used by the index for that column. For example, a B-tree index on
four-byte integers would use the <TT
CLASS="LITERAL"
>int4_ops</TT
> class;
this operator class includes comparison functions for four-byte
integers. In practice the default operator class for the column's data
type is usually sufficient. The main point of having operator classes
is that for some data types, there could be more than one meaningful
ordering. For example, we might want to sort a complex-number data
type either by absolute value or by real part. We could do this by
defining two operator classes for the data type and then selecting
the proper class when making an index. More information about
operator classes is in <A
HREF="indexes-opclass.html"
>Section 11.9</A
> and in <A
HREF="xindex.html"
>Section 35.14</A
>.
</P
><P
> For index methods that support ordered scans (currently, only B-tree),
the optional clauses <TT
CLASS="LITERAL"
>ASC</TT
>, <TT
CLASS="LITERAL"
>DESC</TT
>, <TT
CLASS="LITERAL"
>NULLS
FIRST</TT
>, and/or <TT
CLASS="LITERAL"
>NULLS LAST</TT
> can be specified to modify
the sort ordering of the index. Since an ordered index can be
scanned either forward or backward, it is not normally useful to create a
single-column <TT
CLASS="LITERAL"
>DESC</TT
> index — that sort ordering is already
available with a regular index. The value of these options is that
multicolumn indexes can be created that match the sort ordering requested
by a mixed-ordering query, such as <TT
CLASS="LITERAL"
>SELECT ... ORDER BY x ASC, y
DESC</TT
>. The <TT
CLASS="LITERAL"
>NULLS</TT
> options are useful if you need to support
<SPAN
CLASS="QUOTE"
>"nulls sort low"</SPAN
> behavior, rather than the default <SPAN
CLASS="QUOTE"
>"nulls
sort high"</SPAN
>, in queries that depend on indexes to avoid sorting steps.
</P
><P
> For most index methods, the speed of creating an index is
dependent on the setting of <A
HREF="runtime-config-resource.html#GUC-MAINTENANCE-WORK-MEM"
>maintenance_work_mem</A
>.
Larger values will reduce the time needed for index creation, so long
as you don't make it larger than the amount of memory really available,
which would drive the machine into swapping.
</P
><P
> Use <A
HREF="sql-dropindex.html"
>DROP INDEX</A
>
to remove an index.
</P
><P
> Prior releases of <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> also had an
R-tree index method. This method has been removed because
it had no significant advantages over the GiST method.
If <TT
CLASS="LITERAL"
>USING rtree</TT
> is specified, <TT
CLASS="COMMAND"
>CREATE INDEX</TT
>
will interpret it as <TT
CLASS="LITERAL"
>USING gist</TT
>, to simplify conversion
of old databases to GiST.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN69123"
></A
><H2
>Examples</H2
><P
> To create a B-tree index on the column <TT
CLASS="LITERAL"
>title</TT
> in
the table <TT
CLASS="LITERAL"
>films</TT
>:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE UNIQUE INDEX title_idx ON films (title);</PRE
><P>
</P
><P
> To create an index on the expression <TT
CLASS="LITERAL"
>lower(title)</TT
>,
allowing efficient case-insensitive searches:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE INDEX ON films ((lower(title)));</PRE
><P>
(In this example we have chosen to omit the index name, so the system
will choose a name, typically <TT
CLASS="LITERAL"
>films_lower_idx</TT
>.)
</P
><P
> To create an index with non-default collation:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE INDEX title_idx_german ON films (title COLLATE "de_DE");</PRE
><P>
</P
><P
> To create an index with non-default sort ordering of nulls:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE INDEX title_idx_nulls_low ON films (title NULLS FIRST);</PRE
><P>
</P
><P
> To create an index with non-default fill factor:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE UNIQUE INDEX title_idx ON films (title) WITH (fillfactor = 70);</PRE
><P>
</P
><P
> To create a <ACRONYM
CLASS="ACRONYM"
>GIN</ACRONYM
> index with fast updates disabled:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE INDEX gin_idx ON documents_table USING gin (locations) WITH (fastupdate = off);</PRE
><P>
</P
><P
> To create an index on the column <TT
CLASS="LITERAL"
>code</TT
> in the table
<TT
CLASS="LITERAL"
>films</TT
> and have the index reside in the tablespace
<TT
CLASS="LITERAL"
>indexspace</TT
>:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE INDEX code_idx ON films (code) TABLESPACE indexspace;</PRE
><P>
</P
><P
> To create a GiST index on a point attribute so that we
can efficiently use box operators on the result of the
conversion function:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE INDEX pointloc
ON points USING gist (box(location,location));
SELECT * FROM points
WHERE box(location,location) && '(0,0),(1,1)'::box;</PRE
><P>
</P
><P
> To create an index without locking out writes to the table:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE INDEX CONCURRENTLY sales_quantity_index ON sales_table (quantity);</PRE
><P></P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN69151"
></A
><H2
>Compatibility</H2
><P
> <TT
CLASS="COMMAND"
>CREATE INDEX</TT
> is a
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> language extension. There
are no provisions for indexes in the SQL standard.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN69156"
></A
><H2
>See Also</H2
><A
HREF="sql-alterindex.html"
>ALTER INDEX</A
>, <A
HREF="sql-dropindex.html"
>DROP INDEX</A
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
SUMMARY="Footer navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="sql-creategroup.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="index.html"
ACCESSKEY="H"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="sql-createlanguage.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>CREATE GROUP</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="sql-commands.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>CREATE LANGUAGE</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>