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CREATE
NAME
CREATE FUNCTION - define a new function
SYNOPSIS
CREATE [ OR REPLACE ] FUNCTION
name ( [ [ argmode ] [ argname ] 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 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 can't
change the names or types of any OUT parameters except by dropping the
function.)
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.
The user that creates the function becomes the owner of the function.
PARAMETERS
name The name (optionally schema-qualified) of the function to create.
argmode
The mode of an argument: either IN, OUT, or INOUT. If omitted, the
default is IN.
argname
The name of an argument. Some languages (currently only PL/pgSQL) let
you use the name in the function body. For other languages the name of
an input argument is just extra documentation. But the name of an
output argument is significant, since 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 may be base, composite, or
domain types, or may reference the type of a table column.
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.
The type of a column is referenced by writing
tablename.columnname%TYPE. Using this feature can sometimes help make
a function independent of changes to the definition of a table.
rettype
The return data type (optionally schema-qualified). The return type
may be a base, composite, or domain type, or may reference the type of
a table column. Depending on the implementation language it may also
be allowed to specify ``pseudotypes'' such as cstring.
When there are OUT or INOUT parameters, the RETURNS clause may 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
tablename.columnname%TYPE.
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.
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 may 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(). 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 the documentation.
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.
definition
A string constant 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 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).
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) ...
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 [drop_function(5)] to remove user-defined functions.
It is often helpful to use dollar quoting (see 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.
To be able to define a function, the user must have the USAGE privilege on
the language.
EXAMPLES
Here are some trivial examples to help you get started. For more
information and examples, see 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);
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.
SEE ALSO
ALTER FUNCTION [alter_function(5)], DROP FUNCTION [drop_function(l)], GRANT
[grant(l)], LOAD [load(l)], REVOKE [revoke(l)], createlang [createlang(1)]
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Index for
Section FUNCTION |
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Alphabetical
listing for C |
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Top of
page |
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