Index for Section FUNCTION

Alphabetical listing for C

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CREATE
NAME
  CREATE FUNCTION - define a new function

SYNOPSIS
  CREATE [ OR REPLACE ] FUNCTION name ( [ argtype [, ...] ] )
      RETURNS rettype
    { LANGUAGE langname
      | IMMUTABLE | STABLE | VOLATILE
      | CALLED ON NULL INPUT | RETURNS NULL ON NULL INPUT | STRICT
      | [EXTERNAL] SECURITY INVOKER | [EXTERNAL] SECURITY DEFINER
      | AS 'definition'
      | AS 'obj_file', 'link_symbol'
    } ...
      [ WITH ( attribute [, ...] ) ]

DESCRIPTION
  CREATE FUNCTION defines a new function.  CREATE OR REPLACE FUNCTION will
  either create a new function, or replace an existing definition.

  If a schema name is included, then the function is created in the specified
  schema. Otherwise it is created in the current schema.  The name of the new
  function must not match any existing function with the same argument types
  in the same schema. However, functions of different argument types may
  share a name (this is called overloading).

  To update the definition of an existing function, use CREATE OR REPLACE
  FUNCTION. It is not possible to change the name or argument types of a
  function this way (if you tried, you'd just be creating a new, distinct
  function). Also, CREATE OR REPLACE FUNCTION will not let you change the
  return type of an existing function. To do that, you must drop and recreate
  the function.

  If you drop and then recreate a function, the new function is not the same
  entity as the old; you will break existing rules, views, triggers, etc.
  that referred to the old function. Use CREATE OR REPLACE FUNCTION to change
  a function definition without breaking objects that refer to the function.

  The user that creates the function becomes the owner of the function.

PARAMETERS
  name The name of a function to create.

  argtype
       The data type(s) of the function's arguments (optionally schema-
       qualified), if any. The argument types may be base, complex, or domain
       types, or copy the type of an existing column.

       The type of a column is referenced by writing
       tablename.columnname%TYPE; using this can sometimes help make a
       function independent from changes to the definition of a table.

       Depending on the implementation language it may also be allowed to
       specify ``pseudotypes'' such as cstring.	 Pseudotypes indicate that
       the actual argument type is either incompletely specified, or outside
       the set of ordinary SQL data types.

  rettype
       The return data type (optionally schema-qualified). The return type
       may be specified as a base, complex, or domain type, or may copy the
       type of an existing column. See the description under argtype above on
       how to reference the type of an existing column.

       Depending on the implementation language it may also be allowed to
       specify ``pseudotypes'' such as cstring.	 The SETOF modifier indicates
       that the function will return a set of items, rather than a single
       item.

  langname
       The name of the language that the function is implemented in.  May be
       SQL, C, internal, or the name of a user-defined procedural language.
       (See also createlang [createlang(1)].) For backward compatibility, the
       name may be enclosed by single quotes.

  IMMUTABLE

  STABLE

  VOLATILE
       These attributes inform the system whether it is safe to replace
       multiple evaluations of the function with a single evaluation, for
       run-time optimization. At most one choice should be specified. If none
       of these appear, VOLATILE is the default assumption.

       IMMUTABLE indicates that the function always returns the same result
       when given the same argument values; that is, it does not do database
       lookups or otherwise use information not directly present in its
       argument list. If this option is given, any call of the function with
       all-constant arguments can be immediately replaced with the function
       value.

       STABLE indicates that within a single table scan the function will
       consistently return the same result for the same argument values, but
       that its result could change across SQL statements. This is the
       appropriate selection for functions whose results depend on database
       lookups, parameter variables (such as the current time zone), etc.
       Also note that the current_timestamp family of functions qualify as
       stable, since their values do not change within a transaction.

       VOLATILE indicates that the function value can change even within a
       single table scan, so no optimizations can be made. Relatively few
       database functions are volatile in this sense; some examples are
       random(), currval(), timeofday(). Note that any function that has
       side-effects must be classified volatile, even if its result is quite
       predictable, to prevent calls from being optimized away; an example is
       setval().

  CALLED ON NULL INPUT

  RETURNS NULL ON NULL INPUT

  STRICT
       CALLED ON NULL INPUT (the default) indicates that the function will be
       called normally when some of its arguments are null. It is then the
       function author's responsibility to check for null values if necessary
       and respond appropriately.

       RETURNS NULL ON NULL INPUT or STRICT indicates that the function
       always returns null whenever any of its arguments are null. If this
       parameter is specified, the function is not executed when there are
       null arguments; instead a null result is assumed automatically.

  [EXTERNAL] SECURITY INVOKER

  [EXTERNAL] SECURITY DEFINER
       SECURITY INVOKER indicates that the function is to be executed with
       the privileges of the user that calls it.  That is the default.
       SECURITY DEFINER specifies that the function is to be executed with
       the privileges of the user that created it.

       The key word EXTERNAL is present for SQL conformance but is optional
       since, unlike in SQL, this feature does not only apply to external
       functions.

  definition
       A string defining the function; the meaning depends on the language.
       It may be an internal function name, the path to an object file, an
       SQL command, or text in a procedural language.

  obj_file, link_symbol
       This form of the AS clause is used for dynamically loadable C language
       functions when the function name in the C language source code is not
       the same as the name of the SQL function. The string obj_file is the
       name of the file containing the dynamically loadable object, and
       link_symbol is the function's link symbol, that is, the name of the
       function in the C language source code. If the link symbol is omitted,
       it is assumed to be the same as the name of the SQL function being
       defined.

  attribute
       The historical way to specify optional pieces of information about the
       function. The following attributes may appear here:

       isStrict
	 Equivalent to STRICT or RETURNS NULL ON NULL INPUT

       isCachable
	 isCachable is an obsolete equivalent of IMMUTABLE; it's still
	 accepted for backwards-compatibility reasons.

  Attribute names are not case-sensitive.

NOTES
  Refer to the section called ``User-Defined Functions'' in the documentation
  for further information on writing functions.

  The full SQL type syntax is allowed for input arguments and return value.
  However, some details of the type specification (e.g., the precision field
  for type numeric) are the responsibility of the underlying function
  implementation and are silently swallowed (i.e., not recognized or
  enforced) by the CREATE FUNCTION command.

  PostgreSQL allows function overloading; that is, the same name can be used
  for several different functions so long as they have distinct argument
  types. However, the C names of all functions must be different, so you must
  give overloaded C functions different C names (for example, use the
  argument types as part of the C names).

  When repeated CREATE FUNCTION calls refer to the same object file, the file
  is only loaded once. To unload and reload the file (perhaps during
  development), use the LOAD [load(5)] command.

  Use DROP FUNCTION to remove user-defined functions.

  Any single quotes or backslashes in the function definition must be escaped
  by doubling them.

  To be able to define a function, the user must have the USAGE privilege on
  the language.

EXAMPLES
  Here is a trivial example to help you get started. For more information and
  examples, see the section called ``User-Defined Functions'' in the
  documentation.

  CREATE FUNCTION add(integer, integer) RETURNS integer
      AS 'select $1 + $2;'
      LANGUAGE SQL
      IMMUTABLE
      RETURNS NULL ON NULL INPUT;

COMPATIBILITY
  A CREATE FUNCTION command is defined in SQL99.  The PostgreSQL version is
  similar but not fully compatible. The attributes are not portable, neither
  are the different available languages.

SEE ALSO
  ALTER FUNCTION [alter_function(5)], DROP FUNCTION [drop_function(5)], GRANT
  [grant(5)], LOAD [load(5)], REVOKE [revoke(5)], createlang(1)

Index for Section FUNCTION

Alphabetical listing for C

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