CREATE INDEX(7)		PostgreSQL 9.2.24 Documentation	       CREATE INDEX(7)



NAME
       CREATE_INDEX - define a new index

SYNOPSIS
       CREATE [ UNIQUE ] INDEX [ CONCURRENTLY ] [ name ] ON table_name [ USING method ]
	   ( { column_name | ( expression ) } [ COLLATE collation ] [ opclass ] [ ASC | DESC ] [ NULLS { FIRST | LAST } ] [, ...] )
	   [ WITH ( storage_parameter = value [, ... ] ) ]
	   [ TABLESPACE tablespace_name ]
	   [ WHERE predicate ]

DESCRIPTION
       CREATE INDEX 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).

       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, and
       GIN. 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 Section 11.8, "Partial Indexes", in the
       documentation 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.

       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 -- see
	   Building Indexes Concurrently.

       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. If the name is omitted, PostgreSQL chooses a suitable name
	   based on the parent table's name and the indexed column name(s).

       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 and gin. 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.

       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.

       storage_parameter
	   The name of an index-method-specific storage parameter. See Index
	   Storage Parameters for details.

       tablespace_name
	   The tablespace in which to create the index. If not specified,
	   default_tablespace is consulted, or temp_tablespaces for indexes on
	   temporary tables.

       predicate
	   The constraint expression for a partial index.

   Index 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
	   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.

       GiST indexes additionally accept this parameter:

       BUFFERING
	   Determines whether the buffering build technique described in
	   Section 53.3.1, "GiST buffering build", in the documentation is
	   used to build the index. With OFF it is disabled, with ON it is
	   enabled, and with AUTO it is initially disabled, but turned on
	   on-the-fly once the index size reaches effective_cache_size. The
	   default is AUTO.

       GIN indexes accept a different parameter:

       FASTUPDATE
	   This setting controls usage of the fast update technique described
	   in Section 55.3.1, "GIN Fast Update Technique", in the
	   documentation. It is a Boolean parameter: ON enables fast update,
	   OFF disables it. (Alternative spellings of ON and OFF are allowed
	   as described in Section 18.1, "Setting Parameters", in the
	   documentation.) 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 afterward to ensure the pending list is
	       emptied.

   Building Indexes 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 Chapter 13, Concurrency Control, in the
       documentation) predating the second scan to terminate. 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 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   | Modifiers
	   --------+---------+-----------
	    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. However, since REINDEX does not
       support concurrent builds, this option is unlikely to seem attractive.)

       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 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 CREATE INDEX command can be performed within a
       transaction block, but CREATE INDEX CONCURRENTLY cannot.

NOTES
       See Chapter 11, Indexes, in the documentation for information about
       when indexes can be used, when they are not used, and in which
       particular situations they can be useful.

	   Caution
	   Hash index operations are not presently WAL-logged, so hash indexes
	   might need to be rebuilt with REINDEX 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.

       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 PostgreSQL.) Only B-tree currently
       supports unique indexes.

       An operator class 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 making an index. More information
       about operator classes is in Section 11.9, "Operator Classes and
       Operator Families", in the documentation and in Section 35.14,
       "Interfacing Extensions To Indexes", in the documentation.

       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 -- 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.

       For most index methods, the speed of creating an index is dependent on
       the setting of 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.

       Use DROP INDEX (DROP_INDEX(7)) to remove an index.

       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.

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

	   CREATE UNIQUE INDEX title_idx ON films (title);

       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
       ALTER INDEX (ALTER_INDEX(7)), DROP INDEX (DROP_INDEX(7))



PostgreSQL 9.2.24		  2017-11-06		       CREATE INDEX(7)