CREATE FUNCTION — define a new function
CREATE [ OR REPLACE ] FUNCTION
name ( [ [ argmode ] [ argname ] argtype [ { DEFAULT | = } default_expr ] [, ...] ] )
[ RETURNS rettype
| RETURNS TABLE ( column_name column_type [, ...] ) ]
{ LANGUAGE lang_name
| TRANSFORM { FOR TYPE type_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 }
| COST execution_cost
| ROWS result_rows
| SUPPORT support_function
| SET configuration_parameter { TO value | = value | FROM CURRENT }
| AS 'definition'
| AS 'obj_file', 'link_symbol'
} ...
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.
nameThe 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.
argnameThe 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.)
argtypeThe 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, 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.
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.
WINDOWWINDOW 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.
IMMUTABLESTABLEVOLATILE
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 37.7.
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 the
security_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 40.5.
This option can only be set by the superuser.
CALLED ON NULL INPUTRETURNS NULL ON NULL INPUTSTRICTCALLED 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 DEFINERSECURITY 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.
PARALLELPARALLEL 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 as UNSAFE, which is
the default.
COST execution_costA 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_rowsA 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.
SUPPORT support_functionThe name (optionally schema-qualified) of a planner support function to use for this function. See Section 37.11 for details. You must be superuser to use this option.
configuration_parametervalue
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 and Chapter 19 for more information about allowed parameter names and values.
definitionA 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 string obj_file is the name of the shared
library file containing the compiled C function, and is interpreted
as for the LOAD command. The string
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. 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 37.3 for further information on writing functions.
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.
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.
Here are some trivial examples to help you get started. For more information and examples, see Section 37.3.
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.
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 Section 5.7 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;
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.