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CREATE FUNCTION

   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 36.3 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. 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 36.7.

   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 39.5. 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. For
          information on how to write SECURITY DEFINER functions safely,
          see below.

          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; 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 only in the parallel group leader process.
          PARALLEL SAFE indicates that the function is safe to run in
          parallel mode without restriction, including in parallel worker
          processes.

          Functions should be labeled parallel unsafe if they modify any
          database state, change the transaction state (other than by
          using a subtransaction for error recovery), access sequences
          (e.g., by calling currval) or make persistent changes to
          settings. They should be labeled 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 36.11 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 and Chapter 19 for more information about allowed
          parameter names and values.

   definition
          A string constant defining the function; the meaning depends on
          the language. It can be an internal function name, the path to
          an object file, an SQL command, or text in a procedural
          language.

          It is often helpful to use dollar quoting (see Section 4.1.2.4)
          to write the function definition string, rather than the normal
          single quote syntax. Without dollar quoting, any single quotes
          or backslashes in the function definition must be escaped by
          doubling them.

   obj_file, link_symbol
          This form of the AS clause is used for dynamically loadable C
          language functions when the function name in the C language
          source code is not the same as the name of the SQL function. The
          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.

   If the security definer function intends to create roles, and if it is
   running as a non-superuser, createrole_self_grant should also be set to
   a known value using the SET clause.

   Another point to keep in mind is that by default, execute privilege is
   granted to PUBLIC for newly created functions (see Section 5.8 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, DROP FUNCTION, GRANT, LOAD, REVOKE