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       CREATE_FUNCTION - define a new 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
           | COST execution_cost
           | ROWS result_rows
           | 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.


           The name (optionally schema-qualified) of the function to create.

           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.

           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.)

           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.

           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.

           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

           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.

           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

           The data type of an output column in the RETURNS TABLE syntax.

           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
           (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 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.

           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

           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 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 (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

           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 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.

           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

           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 19 for more information about allowed parameter names and

           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 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(7) 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 38.3 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,

           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 38.3.

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

       Increment an integer, making use of an argument name, in PL/pgSQL:

           CREATE OR REPLACE FUNCTION increment(i integer) RETURNS integer AS $$
                           RETURN i + 1;
           $$ 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.


       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;
                   SELECT  (pwd = $2) INTO passed
                   FROM    pwds
                   WHERE   username = $1;

                   RETURN passed;
           $$  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(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:

           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;


       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.