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CREATE FUNCTION() SQL Commands CREATE FUNCTION()
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
| 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.
If a schema name is included, then the function is created in the specified schema. Other-
wise 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 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 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. 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.
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 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 tablename.columnname%TYPE. Using
this feature can sometimes help make a function independent of changes to the defi-
nition of a table.
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 out-
put 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. Can be SQL, C,
internal, or the name of a user-defined procedural language. For backward compati-
bility, the name can be enclosed by single quotes.
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 appro-
priate selection for functions whose results depend on database lookups, parameter
variables (such as the current time zone), etc. Also note that the current_times-
tamp 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 in 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 nor-
mally 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 speci-
fied value when the function is entered, and then restored to its prior value when
the function exits. SET FROM CURRENT saves the session's current value of the
parameter as the value to be applied when the function is entered.
See SET [set(7)] and in the documentation for more information about allowed param-
eter 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.
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 dynam-
ically 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 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.
NOTES
Refer to 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).
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 per session. To unload and reload the file (perhaps during development), start a new
session.
Use DROP FUNCTION [drop_function(7)] to remove user-defined functions.
It is often helpful to use dollar quoting (see 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.
If a SET clause is attached to a function, then the effects of a SET LOCAL command exe-
cuted inside the function for the same variable are restricted to the function: the con-
figuration parameter's prior value is still restored at function exit. However, an ordi-
nary SET command (without LOCAL) overrides the SET clause, much as it would do for a pre-
vious SET LOCAL command: the effects of such a command will persist after function exit,
unless the current transaction is rolled back.
To be able to define a function, the user must have the USAGE privilege on the language.
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).
EXAMPLES
Here are some trivial examples to help you get started. For more information and examples,
see 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);
WRITING SECURITY DEFINER FUNCTIONS SAFELY
Because a SECURITY DEFINER function is executed with the privileges of the user that cre-
ated 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 pre-
vents malicious users from creating objects that mask objects used by the function. Par-
ticularly 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 [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 selec-
tively. 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 differ-
ent 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(7)], DROP FUNCTION [drop_function(l)], GRANT [grant(l)],
LOAD [load(l)], REVOKE [revoke(l)], createlang [createlang(1)]
SQL - Language Statements 2011-09-22 CREATE FUNCTION()
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On Apache
Under GNU General Public License
2012-05-25 15:29 @38.107.179.236 Crawled by CCBot/1.0 (+http://www.commoncrawl.org/bot.html)