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CREATE FUNCTION(7)               SQL Commands               CREATE FUNCTION(7)



NAME
       CREATE FUNCTION - define a new function


SYNOPSIS
       CREATE [ OR REPLACE ] FUNCTION
           name ( [ [ argmode ] [ argname ] argtype [ { DEFAULT | = } defexpr ] [, ...] ] )
           [ RETURNS rettype
             | RETURNS TABLE ( colname coltype [, ...] ) ]
         { LANGUAGE langname
           | 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.

       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 exist-
       ing function. To do that, you must drop and recreate the function. (When using OUT parameters, that  means  you
       cannot change the names or types of any OUT parameters except by dropping the function.)

       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  argu-
              ments 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 PL/pgSQL, but currently not SQL) let you use the name
              in the function body. For other languages the name of an input argument is just extra documentation. But
              the name of an output argument is significant, since 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 out-
              side the set of ordinary SQL data types.

              The type of a column is referenced by writing tablename.columnname%TYPE.  Using this feature  can  some-
              times help make a function independent of changes to the definition of a table.

       defexpr
              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 tablename.columnname%TYPE.

       colname
              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.

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

       langname
              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 exist-
              ing 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. 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  optimiza-
              tions  can be made. Relatively few database functions are volatile in this sense; some examples are ran-
              dom(), 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 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 neces-
              sary 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 fea-
              ture 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.

              See SET [set(7)] and 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.

       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.

       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-compatibil-
                     ity reasons.

       Attribute names are not case-sensitive.

NOTES
       Refer to in the documentation for further information on writing functions.

       The  full  SQL type syntax is allowed for declaring a function's arguments and return value. However, parenthe-
       sized 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) ....

       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.

       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.

       Use DROP FUNCTION [drop_function(7)] to remove user-defined functions.

       It  is  often helpful to use dollar quoting (see 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.

       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.

       To be able to define a function, the user must have the USAGE privilege on the language.

       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  com-
       mand. You must own the function to replace it (this includes being a member of the owning role).

       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 in the  documen-
       tation.

       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 com-
       plicated 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 [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 [grant(7)], LOAD [load(7)], REVOKE
       [revoke(7)], createlang [createlang(1)]



SQL - Language Statements         2014-02-17                CREATE FUNCTION(7)