CREATE FUNCTION(7)	PostgreSQL 9.2.24 Documentation	    CREATE FUNCTION(7)



NAME
       CREATE_FUNCTION - define a new function

SYNOPSIS
       CREATE [ OR REPLACE ] FUNCTION
	   name ( [ [ argmode ] [ argname ] argtype [ { DEFAULT | = } default_expr ] [, ...] ] )
	   [ RETURNS rettype
	     | RETURNS TABLE ( column_name column_type [, ...] ) ]
	 { LANGUAGE lang_name
	   | WINDOW
	   | IMMUTABLE | STABLE | VOLATILE | [ NOT ] LEAKPROOF
	   | CALLED ON NULL INPUT | RETURNS NULL ON NULL INPUT | STRICT
	   | [ EXTERNAL ] SECURITY INVOKER | [ EXTERNAL ] SECURITY DEFINER
	   | COST execution_cost
	   | ROWS result_rows
	   | SET configuration_parameter { TO value | = value | FROM CURRENT }
	   | 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.
       To be able to define a function, the user must have the USAGE privilege
       on the language.

       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 input argument types in the same schema. However, functions of
       different argument types can share a name (this is called overloading).

       To replace the current 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 would actually 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. (When using OUT
       parameters, that means you cannot change the types of any OUT
       parameters except by dropping the function.)

       When CREATE OR REPLACE FUNCTION is used to replace an existing
       function, the ownership and permissions of the function do not change.
       All other function properties are assigned the values specified or
       implied in the command. You must own the function to replace it (this
       includes being a member of the owning role).

       If you drop and then recreate a function, the new function is not the
       same entity as the old; you will have to drop existing rules, views,
       triggers, etc. that refer to the old function. Use CREATE OR REPLACE
       FUNCTION to change a function definition without breaking objects that
       refer to the function. Also, ALTER FUNCTION can be used to change most
       of the auxiliary properties of an existing function.

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

       To be able to create a function, you must have USAGE privilege on the
       argument types and the return type.

PARAMETERS
       name
	   The name (optionally schema-qualified) of the function to create.

       argmode
	   The mode of an argument: IN, OUT, INOUT, or VARIADIC. If omitted,
	   the default is IN. Only OUT arguments can follow a VARIADIC one.
	   Also, OUT and INOUT arguments cannot be used together with the
	   RETURNS TABLE notation.

       argname
	   The name of an argument. Some languages (including SQL and
	   PL/pgSQL) let you use the name in the function body. For other
	   languages the name of an input argument is just extra
	   documentation, so far as the function itself is concerned; but you
	   can use input argument names when calling a function to improve
	   readability (see Section 4.3, "Calling Functions", in the
	   documentation). In any case, the name of an output argument is
	   significant, because it defines the column name in the result row
	   type. (If you omit the name for an output argument, the system will
	   choose a default column name.)

       argtype
	   The data type(s) of the function's arguments (optionally
	   schema-qualified), if any. The argument types can be base,
	   composite, or domain types, or can reference the type of a table
	   column.

	   Depending on the implementation language it might 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.

	   The type of a column is referenced by writing
	   table_name.column_name%TYPE. Using this feature can sometimes help
	   make a function independent of changes to the definition of a
	   table.

       default_expr
	   An expression to be used as default value if the parameter is not
	   specified. The expression has to be coercible to the argument type
	   of the parameter. Only input (including INOUT) parameters can have
	   a default value. All input parameters following a parameter with a
	   default value must have default values as well.

       rettype
	   The return data type (optionally schema-qualified). The return type
	   can be a base, composite, or domain type, or can reference the type
	   of a table column. Depending on the implementation language it
	   might also be allowed to specify "pseudotypes" such as cstring. If
	   the function is not supposed to return a value, specify void as the
	   return type.

	   When there are OUT or INOUT parameters, the RETURNS clause can be
	   omitted. If present, it must agree with the result type implied by
	   the output parameters: RECORD if there are multiple output
	   parameters, or the same type as the single output parameter.

	   The SETOF modifier indicates that the function will return a set of
	   items, rather than a single item.

	   The type of a column is referenced by writing
	   table_name.column_name%TYPE.

       column_name
	   The name of an output column in the RETURNS TABLE syntax. This is
	   effectively another way of declaring a named OUT parameter, except
	   that RETURNS TABLE also implies RETURNS SETOF.

       column_type
	   The data type of an output column in the RETURNS TABLE syntax.

       lang_name
	   The name of the language that the function is implemented in. Can
	   be SQL, C, internal, or the name of a user-defined procedural
	   language. For backward compatibility, the name can be enclosed by
	   single quotes.

       WINDOW
	   WINDOW indicates that the function is a window function rather than
	   a plain function. This is currently only useful for functions
	   written in C. The WINDOW attribute cannot be changed when replacing
	   an existing function definition.

       IMMUTABLE, STABLE, VOLATILE
	   These attributes inform the query optimizer about the behavior of
	   the function. At most one choice can be specified. If none of these
	   appear, VOLATILE is the default assumption.

	   IMMUTABLE indicates that the function cannot modify the database
	   and 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 the function cannot modify the database, and
	   that within a single table scan it 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. (It is
	   inappropriate for AFTER triggers that wish to query rows modified
	   by the current command.) 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(). But 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().

	   For additional details see Section 35.6, "Function Volatility
	   Categories", in the documentation.

       LEAKPROOF
	   LEAKPROOF indicates that the function has no side effects. It
	   reveals no information about its arguments other than by its return
	   value. For example, a function which throws an error message for
	   some argument values but not others, or which includes the argument
	   values in any error message, is not leakproof. The query planner
	   may push leakproof functions (but not others) into views created
	   with the security_barrier option. See CREATE VIEW (CREATE_VIEW(7))
	   and Section 37.4, "Rules and Privileges", in the documentation.
	   This option can only be set by the superuser.

       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 allowed for SQL conformance, but it is
	   optional since, unlike in SQL, this feature applies to all
	   functions not only external ones.

       execution_cost
	   A positive number giving the estimated execution cost for the
	   function, in units of cpu_operator_cost. If the function returns a
	   set, this is the cost per returned row. If the cost is not
	   specified, 1 unit is assumed for C-language and internal functions,
	   and 100 units for functions in all other languages. Larger values
	   cause the planner to try to avoid evaluating the function more
	   often than necessary.

       result_rows
	   A positive number giving the estimated number of rows that the
	   planner should expect the function to return. This is only allowed
	   when the function is declared to return a set. The default
	   assumption is 1000 rows.

       configuration_parameter, value
	   The SET clause causes the specified configuration parameter to be
	   set to the specified value when the function is entered, and then
	   restored to its prior value when the function exits.	 SET FROM
	   CURRENT saves the value of the parameter that is current when
	   CREATE FUNCTION is executed as the value to be applied when the
	   function is entered.

	   If a SET clause is attached to a function, then the effects of a
	   SET LOCAL command executed inside the function for the same
	   variable are restricted to the function: the configuration
	   parameter's prior value is still restored at function exit.
	   However, an ordinary SET command (without LOCAL) overrides the SET
	   clause, much as it would do for a previous SET LOCAL command: the
	   effects of such a command will persist after function exit, unless
	   the current transaction is rolled back.

	   See SET(7) and Chapter 18, Server Configuration, in the
	   documentation for more information about allowed parameter names
	   and values.

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

	   It is often helpful to use dollar quoting (see Section 4.1.2.4,
	   "Dollar-quoted String Constants", in the documentation) to write
	   the function definition string, rather than the normal single quote
	   syntax. Without dollar quoting, any single quotes or backslashes in
	   the function definition must be escaped by doubling them.

       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.

	   When repeated CREATE FUNCTION calls refer to the same object file,
	   the file is only loaded once per session. To unload and reload the
	   file (perhaps during development), start a new session.

       attribute
	   The historical way to specify optional pieces of information about
	   the function. The following attributes can 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.

       Refer to Section 35.3, "User-defined Functions", in the documentation
       for further information on writing functions.

OVERLOADING
       PostgreSQL allows function overloading; that is, the same name can be
       used for several different functions so long as they have distinct
       input 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).

       Two functions are considered the same if they have the same names and
       input argument types, ignoring any OUT parameters. Thus for example
       these declarations conflict:

	   CREATE FUNCTION foo(int) ...
	   CREATE FUNCTION foo(int, out text) ...

       Functions that have different argument type lists will not be
       considered to conflict at creation time, but if defaults are provided
       they might conflict in use. For example, consider

	   CREATE FUNCTION foo(int) ...
	   CREATE FUNCTION foo(int, int default 42) ...

       A call foo(10) will fail due to the ambiguity about which function
       should be called.

NOTES
       The full SQL type syntax is allowed for declaring a function's
       arguments and return value. However, parenthesized type modifiers
       (e.g., the precision field for type numeric) are discarded by CREATE
       FUNCTION. Thus for example CREATE FUNCTION foo (varchar(10)) ...	 is
       exactly the same as CREATE FUNCTION foo (varchar) ....

       When replacing an existing function with CREATE OR REPLACE FUNCTION,
       there are restrictions on changing parameter names. You cannot change
       the name already assigned to any input parameter (although you can add
       names to parameters that had none before). If there is more than one
       output parameter, you cannot change the names of the output parameters,
       because that would change the column names of the anonymous composite
       type that describes the function's result. These restrictions are made
       to ensure that existing calls of the function do not stop working when
       it is replaced.

       If a function is declared STRICT with a VARIADIC argument, the
       strictness check tests that the variadic array as a whole is non-null.
       The function will still be called if the array has null elements.

EXAMPLES
       Here are some trivial examples to help you get started. For more
       information and examples, see Section 35.3, "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;

       Increment an integer, making use of an argument name, in PL/pgSQL:

	   CREATE OR REPLACE FUNCTION increment(i integer) RETURNS integer AS $$
		   BEGIN
			   RETURN i + 1;
		   END;
	   $$ LANGUAGE plpgsql;

       Return a record containing multiple output parameters:

	   CREATE FUNCTION dup(in int, out f1 int, out f2 text)
	       AS $$ SELECT $1, CAST($1 AS text) || ' is text' $$
	       LANGUAGE SQL;

	   SELECT * FROM dup(42);

       You can do the same thing more verbosely with an explicitly named
       composite type:

	   CREATE TYPE dup_result AS (f1 int, f2 text);

	   CREATE FUNCTION dup(int) RETURNS dup_result
	       AS $$ SELECT $1, CAST($1 AS text) || ' is text' $$
	       LANGUAGE SQL;

	   SELECT * FROM dup(42);

       Another way to return multiple columns is to use a TABLE function:

	   CREATE FUNCTION dup(int) RETURNS TABLE(f1 int, f2 text)
	       AS $$ SELECT $1, CAST($1 AS text) || ' is text' $$
	       LANGUAGE SQL;

	   SELECT * FROM dup(42);

       However, a TABLE function is different from the preceding examples,
       because it actually returns a set of records, not just one record.

WRITING SECURITY DEFINER FUNCTIONS SAFELY
       Because a SECURITY DEFINER function is executed with the privileges of
       the user that created it, care is needed to ensure that the function
       cannot be misused. For security, search_path should be set to exclude
       any schemas writable by untrusted users. This prevents malicious users
       from creating objects that mask objects used by the function.
       Particularly important in this regard is the temporary-table schema,
       which is searched first by default, and is normally writable by anyone.
       A secure arrangement can be had by forcing the temporary schema to be
       searched last. To do this, write pg_temp as the last entry in
       search_path. This function illustrates safe usage:

	   CREATE FUNCTION check_password(uname TEXT, pass TEXT)
	   RETURNS BOOLEAN AS $$
	   DECLARE passed BOOLEAN;
	   BEGIN
		   SELECT  (pwd = $2) INTO passed
		   FROM	   pwds
		   WHERE   username = $1;

		   RETURN passed;
	   END;
	   $$  LANGUAGE plpgsql
	       SECURITY DEFINER
	       -- Set a secure search_path: trusted schema(s), then 'pg_temp'.
	       SET search_path = admin, pg_temp;

       Before PostgreSQL version 8.3, the SET option was not available, and so
       older functions may contain rather complicated logic to save, set, and
       restore search_path. The SET option is far easier to use for this
       purpose.

       Another point to keep in mind is that by default, execute privilege is
       granted to PUBLIC for newly created functions (see GRANT(7) for more
       information). Frequently you will wish to restrict use of a security
       definer function to only some users. To do that, you must revoke the
       default PUBLIC privileges and then grant execute privilege selectively.
       To avoid having a window where the new function is accessible to all,
       create it and set the privileges within a single transaction. For
       example:

	   BEGIN;
	   CREATE FUNCTION check_password(uname TEXT, pass TEXT) ... SECURITY DEFINER;
	   REVOKE ALL ON FUNCTION check_password(uname TEXT, pass TEXT) FROM PUBLIC;
	   GRANT EXECUTE ON FUNCTION check_password(uname TEXT, pass TEXT) TO admins;
	   COMMIT;

COMPATIBILITY
       A CREATE FUNCTION command is defined in SQL:1999 and later. The
       PostgreSQL version is similar but not fully compatible. The attributes
       are not portable, neither are the different available languages.

       For compatibility with some other database systems, argmode can be
       written either before or after argname. But only the first way is
       standard-compliant.

       The SQL standard does not specify parameter defaults. The syntax with
       the DEFAULT key word is from Oracle, and it is somewhat in the spirit
       of the standard: SQL/PSM uses it for variable default values. The
       syntax with = is used in T-SQL and Firebird.

SEE ALSO
       ALTER FUNCTION (ALTER_FUNCTION(7)), DROP FUNCTION (DROP_FUNCTION(7)),
       GRANT(7), LOAD(7), REVOKE(7), createlang(1)



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