Index for Section INDEX

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CREATE
NAME
  CREATE INDEX - define a new index

SYNOPSIS
  CREATE [ UNIQUE ] INDEX index_name ON table
      [ USING acc_method ] ( column [ ops_name ] [, ...] )
      [ WHERE predicate ]
  CREATE [ UNIQUE ] INDEX index_name ON table
      [ USING acc_method ] ( func_name( column [, ... ]) [ ops_name ] )
      [ WHERE predicate ]

  INPUTS

  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.

  index_name
       The name of the index to be created.

  table
       The name of the table to be indexed.

  acc_method
       The name of the access method to be used for the index. The default
       access method is BTREE.	PostgreSQL provides four access methods for
       indexes:

       BTREE
	 an implementation of Lehman-Yao high-concurrency B-trees.

       RTREE
	 implements standard R-trees using Guttman's quadratic split
	 algorithm.

       HASH
	 an implementation of Litwin's linear hashing.

       GIST
	 Generalized Index Search Trees.

  column
       The name of a column of the table.

  ops_name
       An associated operator class. See below for details.

  func_name
       A function, which returns a value that can be indexed.

  predicate
       Defines the constraint expression for a partial index.

  OUTPUTS

  CREATE
       The message returned if the index is successfully created.

  ERROR: Cannot create index: 'index_name' already exists.
       This error occurs if it is impossible to create the index.

DESCRIPTION
  CREATE INDEX constructs an index index_name on the specified table.

       Tip: Indexes are primarily used to enhance database performance.	 But
       inappropriate use will result in slower performance.

  In the first syntax shown above, the key field(s) for the index are
  specified as column names.  Multiple fields can be specified if the index
  access method supports multicolumn indexes.

  In the second syntax shown above, an index is defined on the result of a
  user-specified function func_name applied to one or more columns of a
  single table.	 These functional indexes can be used to obtain fast access
  to data based on operators that would normally require some transformation
  to apply them to the base data.

  PostgreSQL provides B-tree, R-tree, hash, and GiST access methods for
  indexes. The B-tree access method is an implementation of Lehman-Yao high-
  concurrency B-trees. The R-tree access method implements standard R-trees
  using Guttman's quadratic split algorithm.  The hash access method is an
  implementation of Litwin's linear hashing. We mention the algorithms used
  solely to indicate that all of these access methods are fully dynamic and
  do not have to be optimized periodically (as is the case with, for example,
  static hash access methods).

  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 somehow more interesting 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.

  The expression used in the WHERE clause may refer only to columns of the
  underlying table (but it can use all columns, not only the one(s) being
  indexed). Presently, sub-SELECTs and aggregate expressions are also
  forbidden in WHERE.

  All functions and operators used in an index definition must be cachable,
  that is, their results must depend only on their input 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, remember to mark
  the function cachable when you create it.

  Use DROP INDEX [drop_index(5)] to remove an index.

  NOTES

  The PostgreSQL query optimizer will consider using a B-tree index whenever
  an indexed attribute is involved in a comparison using one of: <, <=, =,
  >=, >

  The PostgreSQL query optimizer will consider using an R-tree index whenever
  an indexed attribute is involved in a comparison using one of: <<, &<, &>,
  >>, @, ~=, &&

  The PostgreSQL query optimizer will consider using a hash index whenever an
  indexed attribute is involved in a comparison using the = operator.

  Currently, only the B-tree and gist access methods support multi-column
  indexes. Up to 16 keys may 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 field'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. There are also some operator classes with special
  purposes:

  o+ The operator classes box_ops and bigbox_ops both support R-tree indexes
    on the box data type.  The difference between them is that bigbox_ops
    scales box coordinates down, to avoid floating-point exceptions from
    doing multiplication, addition, and subtraction on very large floating-
    point coordinates. (Note: this was true some time ago, but currently the
    two operator classes both use floating point and are effectively
    identical.)

  The following query shows all defined operator classes:

  SELECT am.amname AS acc_method,
	 opc.opcname AS ops_name,
	 opr.oprname AS ops_comp
      FROM pg_am am, pg_opclass opc, pg_amop amop, pg_operator opr
      WHERE opc.opcamid = am.oid AND
	    amop.amopclaid = opc.oid AND
	    amop.amopopr = opr.oid
      ORDER BY acc_method, ops_name, ops_comp;

USAGE
  To create a B-tree index on the field title in the table films:

  CREATE UNIQUE INDEX title_idx
      ON films (title);

COMPATIBILITY
  SQL92

  CREATE INDEX is a PostgreSQL language extension.

  There is no CREATE INDEX command in SQL92.

Index for Section INDEX

Alphabetical listing for C

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