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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
           | WINDOW
           | 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.
       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 with the
       same input 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 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.

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 (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, 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, "Calling Functions", in the documentation). 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 "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
           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 "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 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. Can
           be SQL, C, internal, or the name of a user-defined procedural
           language. For backward compatibility, the name can be enclosed by
           single quotes.

       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 35.6, "Function Volatility
           Categories", 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 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.

       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 specified 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.

           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 18, Server Configuration, in the
           documentation 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,
           "Dollar-quoted String Constants", 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.

       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.

           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.

       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.

       Refer to Section 35.3, "User-defined Functions", in the documentation
       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. 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) ...

       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 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.

       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 35.3, "User-defined Functions",
       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);

       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 created 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 that mask objects 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 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(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 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.

       The SQL standard does not specify parameter defaults. The syntax with
       the DEFAULT key word is from Oracle, and it is somewhat in the spirit
       of the standard: SQL/PSM uses it for variable default values. The
       syntax with = is used in T-SQL and Firebird.

SEE ALSO

       ALTER FUNCTION (ALTER_FUNCTION(7)), DROP FUNCTION (DROP_FUNCTION(7)),
       GRANT(7), LOAD(7), REVOKE(7), createlang(1)