| | CREATE FUNCTIONNameCREATE FUNCTION -- define a new function SynopsisCREATE [ OR REPLACE ] FUNCTION name ( [ [ argname ] 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 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.
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 (optionally schema-qualified) of the function to create.
- 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
argument name is just extra documentation.
- argtype
The data type(s) of the function's arguments (optionally
schema-qualified), if any. The argument types may be base, complex, or
domains, 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 a base type, complex type, or a domain,
or may be specified to 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.
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
may 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 qualifies
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 constant 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 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.
EnterpriseDB 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.
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.
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;
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