CREATE INDEX

CREATE INDEX

7

SQL - Language Statements

CREATE INDEX

define a new index

CREATE \[ UNIQUE \] INDEX \[ CONCURRENTLY \] \[ \[ IF NOT EXISTS \]

name

\] ON \[ ONLY \]

table\_name

\[ USING

method

\] ( {

column\_name

\| (

expression

) } \[ COLLATE

collation

\] \[

opclass

\[ (

opclass\_parameter

=

value

\[, \... \] ) \] \] \[ ASC \| DESC \] \[ NULLS { FIRST \| LAST } \] \[,
\...\] ) \[ INCLUDE (

column\_name

\[, \...\] ) \] \[ NULLS \[ NOT \] DISTINCT \] \[ WITH (

storage\_parameter

\[=

value

\] \[, \... \] ) \] \[ TABLESPACE

tablespace\_name

\] \[ WHERE

predicate

\]

Description
===========

`CREATE INDEX` constructs an index on the specified column(s) of the
specified relation, which can be a table or a materialized view. Indexes
are primarily used to enhance database performance (though inappropriate
use can result in slower performance).

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.

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 `upper(col)` would allow the clause
`WHERE upper(col) = 'JIM'` to use an index.

PostgreSQL provides the index methods B-tree, hash, GiST, SP-GiST, GIN,
and BRIN. Users can also define their own index methods, but that is
fairly complicated.

When the `WHERE` clause is present, a partial index 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 `WHERE` with `UNIQUE` to enforce
uniqueness over a subset of a table. See [???](#indexes-partial) for
more discussion.

The expression used in the `WHERE` 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 `WHERE`. The same restrictions apply to index fields that
are expressions.

All functions and operators used in an index definition must be
"immutable", 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 `WHERE` clause, remember to mark the function immutable
when you create it.

Parameters
==========

`UNIQUE`

:   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.

    Additional restrictions apply when unique indexes are applied to
    partitioned tables; see [???](#sql-createtable).

`CONCURRENTLY`

:   When this option is used, PostgreSQL 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 MDASH see
    [Building Indexes Concurrently](#sql-createindex-concurrently)
    below.

    For temporary tables, `CREATE INDEX` is always non-concurrent, as no
    other session can access them, and non-concurrent index creation is
    cheaper.

`IF NOT EXISTS`

:   Do not throw an error if a relation with the same name already
    exists. A notice is issued in this case. Note that there is no
    guarantee that the existing index is anything like the one that
    would have been created. Index name is required when `IF NOT EXISTS`
    is specified.

`INCLUDE`

:   The optional `INCLUDE` clause specifies a list of columns which will
    be included in the index as non-key columns. A non-key column cannot
    be used in an index scan search qualification, and it is disregarded
    for purposes of any uniqueness or exclusion constraint enforced by
    the index. However, an index-only scan can return the contents of
    non-key columns without having to visit the index\'s table, since
    they are available directly from the index entry. Thus, addition of
    non-key columns allows index-only scans to be used for queries that
    otherwise could not use them.

    It\'s wise to be conservative about adding non-key columns to an
    index, especially wide columns. If an index tuple exceeds the
    maximum size allowed for the index type, data insertion will fail.
    In any case, non-key columns duplicate data from the index\'s table
    and bloat the size of the index, thus potentially slowing searches.
    Furthermore, B-tree deduplication is never used with indexes that
    have a non-key column.

    Columns listed in the `INCLUDE` clause don\'t need appropriate
    operator classes; the clause can include columns whose data types
    don\'t have operator classes defined for a given access method.

    Expressions are not supported as included columns since they cannot
    be used in index-only scans.

    Currently, the B-tree, GiST and SP-GiST index access methods support
    this feature. In these indexes, the values of columns listed in the
    `INCLUDE` clause are included in leaf tuples which correspond to
    heap tuples, but are not included in upper-level index entries used
    for tree navigation.

name

:   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. The name of the index must be distinct from the name of any
    other relation (table, sequence, index, view, materialized view, or
    foreign table) in that schema. If the name is omitted, PostgreSQL
    chooses a suitable name based on the parent table\'s name and the
    indexed column name(s).

`ONLY`

:   Indicates not to recurse creating indexes on partitions, if the
    table is partitioned. The default is to recurse.

table\_name

:   The name (possibly schema-qualified) of the table to be indexed.

method

:   The name of the index method to be used. Choices are `btree`,
    `hash`, `gist`, `spgist`, `gin`, and `brin`. The default method is
    `btree`.

column\_name

:   The name of a column of the table.

expression

:   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.

collation

:   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.

opclass

:   The name of an operator class. See below for details.

opclass\_parameter

:   The name of an operator class parameter. See below for details.

`ASC`

:   Specifies ascending sort order (which is the default).

`DESC`

:   Specifies descending sort order.

`NULLS FIRST`

:   Specifies that nulls sort before non-nulls. This is the default when
    `DESC` is specified.

`NULLS LAST`

:   Specifies that nulls sort after non-nulls. This is the default when
    `DESC` is not specified.

`NULLS DISTINCT`; `NULLS NOT DISTINCT`

:   Specifies whether for a unique index, null values should be
    considered distinct (not equal). The default is that they are
    distinct, so that a unique index could contain multiple null values
    in a column.

storage\_parameter

:   The name of an index-method-specific storage parameter. See [Index
    Storage Parameters](#sql-createindex-storage-parameters) below for
    details.

tablespace\_name

:   The tablespace in which to create the index. If not specified,
    [???](#guc-default-tablespace) is consulted, or
    [???](#guc-temp-tablespaces) for indexes on temporary tables.

predicate

:   The constraint expression for a partial index.

Index Storage Parameters {#sql-createindex-storage-parameters}
------------------------

The optional `WITH` clause specifies storage parameters 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:

`fillfactor` (`integer`) `fillfactor` storage parameter

:   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 builds, 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 fragmentation of the on-disk index structure.
    B-trees use a default fillfactor of 90, but any integer value from
    10 to 100 can be selected.

    B-tree indexes on tables where many inserts and/or updates are
    anticipated can benefit from lower fillfactor settings at
    `CREATE INDEX` time (following bulk loading into the table). Values
    in the range of 50 - 90 can usefully "smooth out" the *rate* of page
    splits during the early life of the B-tree index (lowering
    fillfactor like this may even lower the absolute number of page
    splits, though this effect is highly workload dependent). The B-tree
    bottom-up index deletion technique described in
    [???](#btree-deletion) is dependent on having some "extra" space on
    pages to store "extra" tuple versions, and so can be affected by
    fillfactor (though the effect is usually not significant).

    In other specific cases it might be useful to increase fillfactor to
    100 at `CREATE INDEX` time as a way of maximizing space utilization.
    You should only consider this when you are completely sure that the
    table is static (i.e. that it will never be affected by either
    inserts or updates). A fillfactor setting of 100 otherwise risks
    *harming* performance: even a few updates or inserts will cause a
    sudden flood of page splits.

    The other index methods use fillfactor in different but roughly
    analogous ways; the default fillfactor varies between methods.

B-tree indexes additionally accept this parameter:

`deduplicate_items` (`boolean`) `deduplicate_items` storage parameter

:   Controls usage of the B-tree deduplication technique described in
    [???](#btree-deduplication). Set to `ON` or `OFF` to enable or
    disable the optimization. (Alternative spellings of `ON` and `OFF`
    are allowed as described in [???](#config-setting).) The default is
    `ON`.

    > **Note**
    >
    > Turning `deduplicate_items` off via `ALTER INDEX` prevents future
    > insertions from triggering deduplication, but does not in itself
    > make existing posting list tuples use the standard tuple
    > representation.

GiST indexes additionally accept this parameter:

`buffering` (`enum`) `buffering` storage parameter

:   Determines whether the buffered build technique described in
    [???](#gist-buffering-build) is used to build the index. With `OFF`
    buffering is disabled, with `ON` it is enabled, and with `AUTO` it
    is initially disabled, but is turned on on-the-fly once the index
    size reaches [???](#guc-effective-cache-size). The default is
    `AUTO`. Note that if sorted build is possible, it will be used
    instead of buffered build unless `buffering=ON` is specified.

GIN indexes accept different parameters:

`fastupdate` (`boolean`) `fastupdate` storage parameter

:   This setting controls usage of the fast update technique described
    in [???](#gin-fast-update). It is a Boolean parameter: `ON` enables
    fast update, `OFF` disables it. The default is `ON`.

    > **Note**
    >
    > Turning `fastupdate` off via `ALTER INDEX` prevents future
    > insertions from going into the list of pending index entries, but
    > does not in itself flush previous entries. You might want to
    > `VACUUM` the table or call `gin_clean_pending_list` function
    > afterward to ensure the pending list is emptied.

<!-- -->

`gin_pending_list_limit` (`integer`) `gin_pending_list_limit` storage parameter

:   Custom [???](#guc-gin-pending-list-limit) parameter. This value is
    specified in kilobytes.

BRIN indexes accept different parameters:

`pages_per_range` (`integer`) `pages_per_range` storage parameter

:   Defines the number of table blocks that make up one block range for
    each entry of a BRIN index (see [???](#brin-intro) for more
    details). The default is `128`.

`autosummarize` (`boolean`) `autosummarize` storage parameter

:   Defines whether a summarization run is invoked for the previous page
    range whenever an insertion is detected on the next one.

Building Indexes Concurrently {#sql-createindex-concurrently}
-----------------------------

index

building concurrently

Creating an index can interfere with regular operation of a database.
Normally PostgreSQL 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.

PostgreSQL supports building indexes without locking out writes. This
method is invoked by specifying the `CONCURRENTLY` option of
`CREATE INDEX`. When this option is used, PostgreSQL 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.

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 [???](#mvcc)) predating the second scan to
terminate, including transactions used by any phase of concurrent index
builds on other tables, if the indexes involved are partial or have
columns that are not simple column references. Then finally the index
can be marked ready for use, and the `CREATE INDEX` 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.

If a problem arises while scanning the table, such as a deadlock or a
uniqueness violation in a unique index, the `CREATE INDEX` command will
fail but leave behind an "invalid" index. This index will be ignored for
querying purposes because it might be incomplete; however it will still
consume update overhead. The psql `\d` command will report such an index
as `INVALID`:

    postgres=# \d tab
           Table "public.tab"
     Column |  Type   | Collation | Nullable | Default 
    --------+---------+-----------+----------+---------
     col    | integer |           |          | 
    Indexes:
        "idx" btree (col) INVALID

The recommended recovery method in such cases is to drop the index and
try again to perform `CREATE INDEX CONCURRENTLY`. (Another possibility
is to rebuild the index with `REINDEX INDEX CONCURRENTLY`).

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
"invalid" index continues to enforce its uniqueness constraint
afterwards.

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.

Regular index builds permit other regular index builds on the same table
to occur simultaneously, but only one concurrent index build can occur
on a table at a time. In either case, schema modification of the table
is not allowed while the index is being built. Another difference is
that a regular `CREATE INDEX` command can be performed within a
transaction block, but `CREATE INDEX CONCURRENTLY` cannot.

Concurrent builds for indexes on partitioned tables are currently not
supported. However, you may concurrently build the index on each
partition individually and then finally create the partitioned index
non-concurrently in order to reduce the time where writes to the
partitioned table will be locked out. In this case, building the
partitioned index is a metadata only operation.

Notes
=====

See [???](#indexes) for information about when indexes can be used, when
they are not used, and in which particular situations they can be
useful.

Currently, only the B-tree, GiST, GIN, and BRIN index methods support
multiple-key-column indexes. Whether there can be multiple key columns
is independent of whether `INCLUDE` columns can be added to the index.
Indexes can have up to 32 columns, including `INCLUDE` columns. (This
limit can be altered when building PostgreSQL.) Only B-tree currently
supports unique indexes.

An operator class with optional parameters 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 `int4_ops` 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 creating an index. More information about operator classes is in
[???](#indexes-opclass) and in [???](#xindex).

When `CREATE INDEX` is invoked on a partitioned table, the default
behavior is to recurse to all partitions to ensure they all have
matching indexes. Each partition is first checked to determine whether
an equivalent index already exists, and if so, that index will become
attached as a partition index to the index being created, which will
become its parent index. If no matching index exists, a new index will
be created and automatically attached; the name of the new index in each
partition will be determined as if no index name had been specified in
the command. If the `ONLY` option is specified, no recursion is done,
and the index is marked invalid. (`ALTER INDEX ... ATTACH PARTITION`
marks the index valid, once all partitions acquire matching indexes.)
Note, however, that any partition that is created in the future using
`CREATE TABLE ... PARTITION OF` will automatically have a matching
index, regardless of whether `ONLY` is specified.

For index methods that support ordered scans (currently, only B-tree),
the optional clauses `ASC`, `DESC`, `NULLS
   FIRST`, and/or `NULLS LAST` 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
`DESC` index MDASH 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 `SELECT ... ORDER BY x ASC, y
   DESC`. The `NULLS` options are useful if you need to support "nulls
sort low" behavior, rather than the default "nulls sort high", in
queries that depend on indexes to avoid sorting steps.

The system regularly collects statistics on all of a table\'s columns.
Newly-created non-expression indexes can immediately use these
statistics to determine an index\'s usefulness. For new expression
indexes, it is necessary to run [`ANALYZE`](#sql-analyze) or wait for
the [autovacuum daemon](#autovacuum) to analyze the table to generate
statistics for these indexes.

For most index methods, the speed of creating an index is dependent on
the setting of [???](#guc-maintenance-work-mem). 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.

PostgreSQL can build indexes while leveraging multiple CPUs in order to
process the table rows faster. This feature is known as parallel index
build. For index methods that support building indexes in parallel
(currently, only B-tree), `maintenance_work_mem` specifies the maximum
amount of memory that can be used by each index build operation as a
whole, regardless of how many worker processes were started. Generally,
a cost model automatically determines how many worker processes should
be requested, if any.

Parallel index builds may benefit from increasing `maintenance_work_mem`
where an equivalent serial index build will see little or no benefit.
Note that `maintenance_work_mem` may influence the number of worker
processes requested, since parallel workers must have at least a `32MB`
share of the total `maintenance_work_mem` budget. There must also be a
remaining `32MB` share for the leader process. Increasing
[???](#guc-max-parallel-maintenance-workers) may allow more workers to
be used, which will reduce the time needed for index creation, so long
as the index build is not already I/O bound. Of course, there should
also be sufficient CPU capacity that would otherwise lie idle.

Setting a value for `parallel_workers` via
[`ALTER TABLE`](#sql-altertable) directly controls how many parallel
worker processes will be requested by a `CREATE
   INDEX` against the table. This bypasses the cost model completely,
and prevents `maintenance_work_mem` from affecting how many parallel
workers are requested. Setting `parallel_workers` to 0 via `ALTER
   TABLE` will disable parallel index builds on the table in all cases.

> **Tip**
>
> You might want to reset `parallel_workers` after setting it as part of
> tuning an index build. This avoids inadvertent changes to query plans,
> since `parallel_workers` affects *all* parallel table scans.

While `CREATE INDEX` with the `CONCURRENTLY` option supports parallel
builds without special restrictions, only the first table scan is
actually performed in parallel.

Use [`DROP INDEX`](#sql-dropindex) to remove an index.

Like any long-running transaction, `CREATE INDEX` on a table can affect
which tuples can be removed by concurrent `VACUUM` on any other table.
Excepted from this are operations with the `CONCURRENTLY` option for
indexes that are not partial and do not index any expressions.

Prior releases of PostgreSQL also had an R-tree index method. This
method has been removed because it had no significant advantages over
the GiST method. If `USING rtree` is specified, `CREATE INDEX` will
interpret it as `USING gist`, to simplify conversion of old databases to
GiST.

Each backend running `CREATE INDEX` will report its progress in the
pg\_stat\_progress\_create\_index view. See
[???](#create-index-progress-reporting) for details.

Examples
========

To create a unique B-tree index on the column `title` in the table
`films`:

    CREATE UNIQUE INDEX title_idx ON films (title);

To create a unique B-tree index on the column `title` with included
columns `director` and `rating` in the table `films`:

    CREATE UNIQUE INDEX title_idx ON films (title) INCLUDE (director, rating);

To create a B-Tree index with deduplication disabled:

    CREATE INDEX title_idx ON films (title) WITH (deduplicate_items = off);

To create an index on the expression `lower(title)`, allowing efficient
case-insensitive searches:

    CREATE INDEX ON films ((lower(title)));

(In this example we have chosen to omit the index name, so the system
will choose a name, typically `films_lower_idx`.)

To create an index with non-default collation:

    CREATE INDEX title_idx_german ON films (title COLLATE "de_DE");

To create an index with non-default sort ordering of nulls:

    CREATE INDEX title_idx_nulls_low ON films (title NULLS FIRST);

To create an index with non-default fill factor:

    CREATE UNIQUE INDEX title_idx ON films (title) WITH (fillfactor = 70);

To create a GIN index with fast updates disabled:

    CREATE INDEX gin_idx ON documents_table USING GIN (locations) WITH (fastupdate = off);

To create an index on the column `code` in the table `films` and have
the index reside in the tablespace `indexspace`:

    CREATE INDEX code_idx ON films (code) TABLESPACE indexspace;

To create a GiST index on a point attribute so that we can efficiently
use box operators on the result of the conversion function:

    CREATE INDEX pointloc
        ON points USING gist (box(location,location));
    SELECT * FROM points
        WHERE box(location,location) && '(0,0),(1,1)'::box;

To create an index without locking out writes to the table:

    CREATE INDEX CONCURRENTLY sales_quantity_index ON sales_table (quantity);

Compatibility
=============

`CREATE INDEX` is a PostgreSQL language extension. There are no
provisions for indexes in the SQL standard.

See Also
========
