phpman > man > CREATE_FUNCTION(7)

CREATE FUNCTION(7)                 PostgreSQL 14.23 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
           | 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'
           | sql_body
         } ...

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.

       Refer to Section 38.3 for further information on writing functions.

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). 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. 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 “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. The default is sql if
           sql_body is specified. 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 (CREATE_TRANSFORM(7)).
           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. 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 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 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 (CREATE_VIEW(7)) 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 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 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 as
           UNSAFE, 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.

       SUPPORT support_function
           The name (optionally schema-qualified) of a planner support function to use for this
           function. See Section 38.11 for details. You must be superuser to use this option.

       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 20 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 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.

       sql_body
           The body of a LANGUAGE SQL function. This can either be a single statement

               RETURN expression

           or a block

               BEGIN ATOMIC
                 statement;
                 statement;
                 ...
                 statement;
               END

           This is similar to writing the text of the function body as a string constant (see
           definition above), but there are some differences: This form only works for LANGUAGE SQL,
           the string constant form works for all languages. This form is parsed at function
           definition time, the string constant form is parsed at execution time; therefore this
           form cannot support polymorphic argument types and other constructs that are not
           resolvable at function definition time. This form tracks dependencies between the
           function and objects used in the function body, so DROP ... CASCADE will work correctly,
           whereas the form using string literals may leave dangling functions. Finally, this form
           is more compatible with the SQL standard and other SQL implementations.

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
       Add two integers using an SQL function:

           CREATE FUNCTION add(integer, integer) RETURNS integer
               AS 'select $1 + $2;'
               LANGUAGE SQL
               IMMUTABLE
               RETURNS NULL ON NULL INPUT;

       The same function written in a more SQL-conforming style, using argument names and an
       unquoted body:

           CREATE FUNCTION add(a integer, b integer) RETURNS integer
               LANGUAGE SQL
               IMMUTABLE
               RETURNS NULL ON NULL INPUT
               RETURN a + b;

       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 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;

COMPATIBILITY
       A CREATE FUNCTION command is defined in the SQL standard. The PostgreSQL implementation can
       be used in a compatible way but has many extensions. Conversely, the SQL standard specifies a
       number of optional features that are not implemented in PostgreSQL.

       The following are important compatibility issues:

       •   OR REPLACE is a PostgreSQL extension.

       •   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.

       •   The SETOF modifier is a PostgreSQL extension.

       •   Only SQL is standardized as a language.

       •   All other attributes except CALLED ON NULL INPUT and RETURNS NULL ON NULL INPUT are not
           standardized.

       •   For the body of LANGUAGE SQL functions, the SQL standard only specifies the sql_body
           form.

       Simple LANGUAGE SQL functions can be written in a way that is both standard-conforming and
       portable to other implementations. More complex functions using advanced features,
       optimization attributes, or other languages will necessarily be specific to PostgreSQL in a
       significant way.

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



PostgreSQL 14.23                                2026                              CREATE FUNCTION(7)