CREATE FUNCTION
CREATE FUNCTION
CREATE FUNCTION - define a new function
Synopsis
CREATE [ OR REPLACE ] FUNCTIONname
( [ [argmode
] [argname
]argtype
[ { DEFAULT | = }default_expr
] [, ...] ] ) [ RETURNSrettype
| RETURNS TABLE (column_name
column_type
[, ...] ) ] { LANGUAGElang_name
| TRANSFORM { FOR TYPEtype_name
} [, ... ] | WINDOW | IMMUTABLE | STABLE | VOLATILE | [ NOT ] LEAKPROOF | CALLED ON NULL INPUT | RETURNS NULL ON NULL INPUT | STRICT | [ EXTERNAL ] SECURITY INVOKER | [ EXTERNAL ] SECURITY DEFINER | PARALLEL { UNSAFE | RESTRICTED | SAFE } | COSTexecution_cost
| ROWSresult_rows
| SETconfiguration_parameter
{ TOvalue
| =value
| FROM CURRENT } | AS 'definition
' | AS 'obj_file
', 'link_symbol
' } ...
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 or procedure with the same input argument types in the same schema. However, functions and procedures 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
, orVARIADIC
. If omitted, the default isIN
. OnlyOUT
arguments can follow aVARIADIC
one. Also,OUT
andINOUT
arguments cannot be used together with theRETURNS 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 ). 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 " pseudo-types " such as
cstring
. Pseudo-types 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 -
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 " pseudo-types " such as
cstring
. If the function is not supposed to return a value, specifyvoid
as the return type.When there are
OUT
orINOUT
parameters, theRETURNS
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 namedOUT
parameter, except thatRETURNS TABLE
also impliesRETURNS 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. It can be
sql
,c
,internal
, or the name of a user-defined procedural language, e.g.,plpgsql
. Enclosing the name in single quotes is deprecated and requires matching case. -
TRANSFORM { FOR TYPE
type_name
} [, ... ] } -
Lists which transforms a call to the function should apply. Transforms convert between SQL types and language-specific data types; see CREATE TRANSFORM . Procedural language implementations usually have hardcoded knowledge of the built-in types, so those don't need to be listed here. If a procedural language implementation does not know how to handle a type and no transform is supplied, it will fall back to a default behavior for converting data types, but this depends on the implementation.
-
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. TheWINDOW
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 forAFTER
triggers that wish to query rows modified by the current command.) Also note that thecurrent_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 arerandom()
,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 issetval()
.For additional details see Section 38.7 .
-
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. This affects how the system executes queries against views created with thesecurity_barrier
option or tables with row level security enabled. The system will enforce conditions from security policies and security barrier views before any user-supplied conditions from the query itself that contain non-leakproof functions, in order to prevent the inadvertent exposure of data. Functions and operators marked as leakproof are assumed to be trustworthy, and may be executed before conditions from security policies and security barrier views. In addition, functions which do not take arguments or which are not passed any arguments from the security barrier view or table do not have to be marked as leakproof to be executed before security conditions. See CREATE VIEW and Section 41.5 . 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
orSTRICT
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 owns 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. -
PARALLEL
-
PARALLEL UNSAFE
indicates that the function can't be executed in parallel mode and the presence of such a function in an SQL statement forces a serial execution plan. This is the default.PARALLEL RESTRICTED
indicates that the function can be executed in parallel mode, but the execution is restricted to parallel group leader.PARALLEL SAFE
indicates that the function is safe to run in parallel mode without restriction.Functions should be labeled parallel unsafe if they modify any database state, or if they make changes to the transaction such as using sub-transactions, or if they access sequences or attempt to make persistent changes to settings (e.g.,
setval
). They should be labeled as parallel restricted if they access temporary tables, client connection state, cursors, prepared statements, or miscellaneous backend-local state which the system cannot synchronize in parallel mode (e.g.,setseed
cannot be executed other than by the group leader because a change made by another process would not be reflected in the leader). In general, if a function is labeled as being safe when it is restricted or unsafe, or if it is labeled as being restricted when it is in fact unsafe, it may throw errors or produce wrong answers when used in a parallel query. C-language functions could in theory exhibit totally undefined behavior if mislabeled, since there is no way for the system to protect itself against arbitrary C code, but in most likely cases the result will be no worse than for any other function. If in doubt, functions should be labeled asUNSAFE
, which is the default. -
COST
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.
-
ROWS
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 whenCREATE 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 aSET 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 ordinarySET
command (withoutLOCAL
) overrides theSET
clause, much as it would do for a previousSET LOCAL
command: the effects of such a command will persist after function exit, unless the current transaction is rolled back.See SET and Chapter 19 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 ) 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 stringobj_file
is the name of the shared library file containing the compiled C function, and is interpreted as for the LOAD command. The stringlink_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. 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 per session. To unload and reload the file (perhaps during development), start a new session.
Refer to Section 38.3 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. Whether or not you use it, this capability entails security precautions when calling functions in databases where some users mistrust other users; see Section 10.3 .
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 38.3 .
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 owns 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 (e.g., tables, functions, and
operators) that mask objects intended to be 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 obtained
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;
This function's intention is to access a table
admin.pwds
.
But without the
SET
clause, or with a
SET
clause
mentioning only
admin
, the function could be subverted by
creating a temporary table named
pwds
.
Before
PostgreSQL
version 8.3, the
SET
clause was not available, and so older functions may
contain rather complicated logic to save, set, and restore
search_path
. The
SET
clause 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
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 the SQL standard.
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.
For parameter defaults, the SQL standard specifies only the syntax with
the
DEFAULT
key word. The syntax
with
=
is used in T-SQL and Firebird.