PostgreSQL 7.4beta4 Documentation
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# CREATE FUNCTION

## Name

CREATE FUNCTION -- define a new function

## Synopsis

    CREATE [ OR REPLACE ] FUNCTION name ( [ argtype [, ...] ] )
        RETURNS rettype
      { LANGUAGE langname
        | IMMUTABLE | STABLE | VOLATILE
        | CALLED ON NULL INPUT | RETURNS NULL ON NULL INPUT | STRICT
        | [EXTERNAL] SECURITY INVOKER | [EXTERNAL] SECURITY DEFINER
        | 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 argument types in the same schema. However, functions of different argument types may share a name (this is called overloading).

To update the 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'd just 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.

If you drop and then recreate a function, the new function is not the same entity as the old; you will break existing rules, views, triggers, etc. that referred to the old function. Use `CREATE OR REPLACE FUNCTION` to change a function definition without breaking objects that refer to the function.

The user that creates the function becomes the owner of the function.

## Parameters

name

  The name of a function to create.

argtype

  The data type(s) of the function's arguments (optionally schema-qualified), if any. The argument types may be base, complex, or domain types, or copy the type of an existing column.

  The type of a column is referenced by writing tablename.columnname%TYPE; using this can sometimes help make a function independent from changes to the definition of a table.

  Depending on the implementation language it may 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.

rettype

  The return data type (optionally schema-qualified). The return type may be specified as a base, complex, or domain type, or may copy the type of an existing column. See the description under argtype above on how to reference the type of an existing column.

  Depending on the implementation language it may also be allowed to specify "pseudotypes" such as `cstring`. The SETOF modifier indicates that the function will return a set of items, rather than a single item.

langname

  The name of the language that the function is implemented in. May be SQL, C, internal, or the name of a user-defined procedural language. (See also createlang.) For backward compatibility, the name may be enclosed by single quotes.

IMMUTABLE
STABLE
VOLATILE

  These attributes inform the system whether it is safe to replace multiple evaluations of the function with a single evaluation, for run-time optimization. At most one choice should be specified. If none of these appear, VOLATILE is the default assumption.

  IMMUTABLE indicates that the function 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 within a single table scan the function 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 optimizations can be made. Relatively few database functions are volatile in this sense; some examples are random(), currval(), timeofday(). 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().

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 present for SQL conformance but is optional since, unlike in SQL, this feature does not only apply to external functions.

definition

  A string defining the function; the meaning depends on the language. It may 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 may 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.

## Notes

Refer to Section 33.3 for further information on writing functions.

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.

PostgreSQL allows function overloading; that is, the same name can be used for several different functions so long as they have distinct 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).

When repeated `CREATE FUNCTION` calls refer to the same object file, the file is only loaded once. To unload and reload the file (perhaps during development), use the LOAD command.

Use `DROP FUNCTION` to remove user-defined functions.

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

## Examples

Here is a trivial example to help you get started. For more information and examples, see Section 33.3.

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

## Compatibility

A `CREATE FUNCTION` command is defined in SQL99. The PostgreSQL version is similar but not fully compatible. The attributes are not portable, neither are the different available languages.

## See Also

ALTER FUNCTION, DROP FUNCTION, GRANT, LOAD, REVOKE, createlang

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