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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>CREATE FUNCTION</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="sql-createforeigntable.html" title="CREATE FOREIGN TABLE" /><link rel="next" href="sql-creategroup.html" title="CREATE GROUP" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">CREATE FUNCTION</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="sql-createforeigntable.html" title="CREATE FOREIGN TABLE">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="sql-commands.html" title="SQL Commands">Up</a></td><th width="60%" align="center">SQL Commands</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 15.6 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="sql-creategroup.html" title="CREATE GROUP">Next</a></td></tr></table><hr /></div><div class="refentry" id="SQL-CREATEFUNCTION"><div class="titlepage"></div><a id="id-1.9.3.67.1" class="indexterm"></a><div class="refnamediv"><h2><span class="refentrytitle">CREATE FUNCTION</span></h2><p>CREATE FUNCTION — define a new function</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><pre class="synopsis">
CREATE [ OR REPLACE ] FUNCTION
<em class="replaceable"><code>name</code></em> ( [ [ <em class="replaceable"><code>argmode</code></em> ] [ <em class="replaceable"><code>argname</code></em> ] <em class="replaceable"><code>argtype</code></em> [ { DEFAULT | = } <em class="replaceable"><code>default_expr</code></em> ] [, ...] ] )
[ RETURNS <em class="replaceable"><code>rettype</code></em>
| RETURNS TABLE ( <em class="replaceable"><code>column_name</code></em> <em class="replaceable"><code>column_type</code></em> [, ...] ) ]
{ LANGUAGE <em class="replaceable"><code>lang_name</code></em>
| TRANSFORM { FOR TYPE <em class="replaceable"><code>type_name</code></em> } [, ... ]
| 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 <em class="replaceable"><code>execution_cost</code></em>
| ROWS <em class="replaceable"><code>result_rows</code></em>
| SUPPORT <em class="replaceable"><code>support_function</code></em>
| SET <em class="replaceable"><code>configuration_parameter</code></em> { TO <em class="replaceable"><code>value</code></em> | = <em class="replaceable"><code>value</code></em> | FROM CURRENT }
| AS '<em class="replaceable"><code>definition</code></em>'
| AS '<em class="replaceable"><code>obj_file</code></em>', '<em class="replaceable"><code>link_symbol</code></em>'
| <em class="replaceable"><code>sql_body</code></em>
} ...
</pre></div><div class="refsect1" id="SQL-CREATEFUNCTION-DESCRIPTION"><h2>Description</h2><p>
<code class="command">CREATE FUNCTION</code> defines a new function.
<code class="command">CREATE OR REPLACE FUNCTION</code> will either create a
new function, or replace an existing definition.
To be able to define a function, the user must have the
<code class="literal">USAGE</code> privilege on the language.
</p><p>
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 <em class="firstterm">overloading</em>).
</p><p>
To replace the current definition of an existing function, use
<code class="command">CREATE OR REPLACE FUNCTION</code>. 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, <code class="command">CREATE OR REPLACE FUNCTION</code> will not let
you change the return type of an existing function. To do that,
you must drop and recreate the function. (When using <code class="literal">OUT</code>
parameters, that means you cannot change the types of any
<code class="literal">OUT</code> parameters except by dropping the function.)
</p><p>
When <code class="command">CREATE OR REPLACE FUNCTION</code> 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).
</p><p>
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
<code class="command">CREATE OR REPLACE FUNCTION</code> to change a function
definition without breaking objects that refer to the function.
Also, <code class="command">ALTER FUNCTION</code> can be used to change most of the
auxiliary properties of an existing function.
</p><p>
The user that creates the function becomes the owner of the function.
</p><p>
To be able to create a function, you must have <code class="literal">USAGE</code>
privilege on the argument types and the return type.
</p><p>
Refer to <a class="xref" href="xfunc.html" title="38.3. User-Defined Functions">Section 38.3</a> for further information on writing
functions.
</p></div><div class="refsect1" id="id-1.9.3.67.6"><h2>Parameters</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><em class="replaceable"><code>name</code></em></span></dt><dd><p>
The name (optionally schema-qualified) of the function to create.
</p></dd><dt><span class="term"><em class="replaceable"><code>argmode</code></em></span></dt><dd><p>
The mode of an argument: <code class="literal">IN</code>, <code class="literal">OUT</code>,
<code class="literal">INOUT</code>, or <code class="literal">VARIADIC</code>.
If omitted, the default is <code class="literal">IN</code>.
Only <code class="literal">OUT</code> arguments can follow a <code class="literal">VARIADIC</code> one.
Also, <code class="literal">OUT</code> and <code class="literal">INOUT</code> arguments cannot be used
together with the <code class="literal">RETURNS TABLE</code> notation.
</p></dd><dt><span class="term"><em class="replaceable"><code>argname</code></em></span></dt><dd><p>
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 <a class="xref" href="sql-syntax-calling-funcs.html" title="4.3. Calling Functions">Section 4.3</a>). 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.)
</p></dd><dt><span class="term"><em class="replaceable"><code>argtype</code></em></span></dt><dd><p>
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.
</p><p>
Depending on the implementation language it might also be allowed
to specify <span class="quote">“<span class="quote">pseudo-types</span>”</span> such as <code class="type">cstring</code>.
Pseudo-types indicate that the actual argument type is either
incompletely specified, or outside the set of ordinary SQL data types.
</p><p>
The type of a column is referenced by writing
<code class="literal"><em class="replaceable"><code>table_name</code></em>.<em class="replaceable"><code>column_name</code></em>%TYPE</code>.
Using this feature can sometimes help make a function independent of
changes to the definition of a table.
</p></dd><dt><span class="term"><em class="replaceable"><code>default_expr</code></em></span></dt><dd><p>
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 <code class="literal">INOUT</code>) parameters can have a default
value. All input parameters following a
parameter with a default value must have default values as well.
</p></dd><dt><span class="term"><em class="replaceable"><code>rettype</code></em></span></dt><dd><p>
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 <span class="quote">“<span class="quote">pseudo-types</span>”</span> such as <code class="type">cstring</code>.
If the function is not supposed to return a value, specify
<code class="type">void</code> as the return type.
</p><p>
When there are <code class="literal">OUT</code> or <code class="literal">INOUT</code> parameters,
the <code class="literal">RETURNS</code> clause can be omitted. If present, it
must agree with the result type implied by the output parameters:
<code class="literal">RECORD</code> if there are multiple output parameters, or
the same type as the single output parameter.
</p><p>
The <code class="literal">SETOF</code>
modifier indicates that the function will return a set of
items, rather than a single item.
</p><p>
The type of a column is referenced by writing
<code class="literal"><em class="replaceable"><code>table_name</code></em>.<em class="replaceable"><code>column_name</code></em>%TYPE</code>.
</p></dd><dt><span class="term"><em class="replaceable"><code>column_name</code></em></span></dt><dd><p>
The name of an output column in the <code class="literal">RETURNS TABLE</code>
syntax. This is effectively another way of declaring a named
<code class="literal">OUT</code> parameter, except that <code class="literal">RETURNS TABLE</code>
also implies <code class="literal">RETURNS SETOF</code>.
</p></dd><dt><span class="term"><em class="replaceable"><code>column_type</code></em></span></dt><dd><p>
The data type of an output column in the <code class="literal">RETURNS TABLE</code>
syntax.
</p></dd><dt><span class="term"><em class="replaceable"><code>lang_name</code></em></span></dt><dd><p>
The name of the language that the function is implemented in.
It can be <code class="literal">sql</code>, <code class="literal">c</code>,
<code class="literal">internal</code>, or the name of a user-defined
procedural language, e.g., <code class="literal">plpgsql</code>. The default is
<code class="literal">sql</code> if <em class="replaceable"><code>sql_body</code></em> is specified. Enclosing the
name in single quotes is deprecated and requires matching case.
</p></dd><dt><span class="term"><code class="literal">TRANSFORM { FOR TYPE <em class="replaceable"><code>type_name</code></em> } [, ... ] }</code></span></dt><dd><p>
Lists which transforms a call to the function should apply. Transforms
convert between SQL types and language-specific data types;
see <a class="xref" href="sql-createtransform.html" title="CREATE TRANSFORM"><span class="refentrytitle">CREATE TRANSFORM</span></a>. 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.
</p></dd><dt><span class="term"><code class="literal">WINDOW</code></span></dt><dd><p><code class="literal">WINDOW</code> indicates that the function is a
<em class="firstterm">window function</em> rather than a plain function.
This is currently only useful for functions written in C.
The <code class="literal">WINDOW</code> attribute cannot be changed when
replacing an existing function definition.
</p></dd><dt><span class="term"><code class="literal">IMMUTABLE</code><br /></span><span class="term"><code class="literal">STABLE</code><br /></span><span class="term"><code class="literal">VOLATILE</code></span></dt><dd><p>
These attributes inform the query optimizer about the behavior
of the function. At most one choice
can be specified. If none of these appear,
<code class="literal">VOLATILE</code> is the default assumption.
</p><p><code class="literal">IMMUTABLE</code> 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.
</p><p><code class="literal">STABLE</code> 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 <code class="literal">AFTER</code> triggers that wish to
query rows modified by the current command.) Also note
that the <code class="function">current_timestamp</code> family of functions qualify
as stable, since their values do not change within a transaction.
</p><p><code class="literal">VOLATILE</code> 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 <code class="literal">random()</code>, <code class="literal">currval()</code>,
<code class="literal">timeofday()</code>. 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
<code class="literal">setval()</code>.
</p><p>
For additional details see <a class="xref" href="xfunc-volatility.html" title="38.7. Function Volatility Categories">Section 38.7</a>.
</p></dd><dt><span class="term"><code class="literal">LEAKPROOF</code></span></dt><dd><p>
<code class="literal">LEAKPROOF</code> 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
<code class="literal">security_barrier</code> 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
<a class="xref" href="sql-createview.html" title="CREATE VIEW"><span class="refentrytitle">CREATE VIEW</span></a> and <a class="xref" href="rules-privileges.html" title="41.5. Rules and Privileges">Section 41.5</a>.
This option can only be set by the superuser.
</p></dd><dt><span class="term"><code class="literal">CALLED ON NULL INPUT</code><br /></span><span class="term"><code class="literal">RETURNS NULL ON NULL INPUT</code><br /></span><span class="term"><code class="literal">STRICT</code></span></dt><dd><p><code class="literal">CALLED ON NULL INPUT</code> (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.
</p><p><code class="literal">RETURNS NULL ON NULL INPUT</code> or
<code class="literal">STRICT</code> 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.
</p></dd><dt><span class="term"><code class="literal">[<span class="optional">EXTERNAL</span>] SECURITY INVOKER</code><br /></span><span class="term"><code class="literal">[<span class="optional">EXTERNAL</span>] SECURITY DEFINER</code></span></dt><dd><p><code class="literal">SECURITY INVOKER</code> indicates that the function
is to be executed with the privileges of the user that calls it.
That is the default. <code class="literal">SECURITY DEFINER</code>
specifies that the function is to be executed with the
privileges of the user that owns it.
</p><p>
The key word <code class="literal">EXTERNAL</code> is allowed for SQL
conformance, but it is optional since, unlike in SQL, this feature
applies to all functions not only external ones.
</p></dd><dt><span class="term"><code class="literal">PARALLEL</code></span></dt><dd><p><code class="literal">PARALLEL UNSAFE</code> 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. <code class="literal">PARALLEL RESTRICTED</code> indicates that
the function can be executed in parallel mode, but the execution is
restricted to parallel group leader. <code class="literal">PARALLEL SAFE</code>
indicates that the function is safe to run in parallel mode without
restriction.
</p><p>
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., <code class="literal">setval</code>). 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., <code class="literal">setseed</code> 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 <code class="literal">UNSAFE</code>, which is
the default.
</p></dd><dt><span class="term"><code class="literal">COST</code> <em class="replaceable"><code>execution_cost</code></em></span></dt><dd><p>
A positive number giving the estimated execution cost for the function,
in units of <a class="xref" href="runtime-config-query.html#GUC-CPU-OPERATOR-COST">cpu_operator_cost</a>. 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.
</p></dd><dt><span class="term"><code class="literal">ROWS</code> <em class="replaceable"><code>result_rows</code></em></span></dt><dd><p>
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.
</p></dd><dt><span class="term"><code class="literal">SUPPORT</code> <em class="replaceable"><code>support_function</code></em></span></dt><dd><p>
The name (optionally schema-qualified) of a <em class="firstterm">planner support
function</em> to use for this function. See
<a class="xref" href="xfunc-optimization.html" title="38.11. Function Optimization Information">Section 38.11</a> for details.
You must be superuser to use this option.
</p></dd><dt><span class="term"><em class="replaceable"><code>configuration_parameter</code></em><br /></span><span class="term"><em class="replaceable"><code>value</code></em></span></dt><dd><p>
The <code class="literal">SET</code> 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.
<code class="literal">SET FROM CURRENT</code> saves the value of the parameter that
is current when <code class="command">CREATE FUNCTION</code> is executed as the value
to be applied when the function is entered.
</p><p>
If a <code class="literal">SET</code> clause is attached to a function, then
the effects of a <code class="command">SET LOCAL</code> 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
<code class="command">SET</code> command (without <code class="literal">LOCAL</code>) overrides the
<code class="literal">SET</code> clause, much as it would do for a previous <code class="command">SET
LOCAL</code> command: the effects of such a command will persist after
function exit, unless the current transaction is rolled back.
</p><p>
See <a class="xref" href="sql-set.html" title="SET"><span class="refentrytitle">SET</span></a> and
<a class="xref" href="runtime-config.html" title="Chapter 20. Server Configuration">Chapter 20</a>
for more information about allowed parameter names and values.
</p></dd><dt><span class="term"><em class="replaceable"><code>definition</code></em></span></dt><dd><p>
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.
</p><p>
It is often helpful to use dollar quoting (see <a class="xref" href="sql-syntax-lexical.html#SQL-SYNTAX-DOLLAR-QUOTING" title="4.1.2.4. Dollar-Quoted String Constants">Section 4.1.2.4</a>) 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.
</p></dd><dt><span class="term"><code class="literal"><em class="replaceable"><code>obj_file</code></em>, <em class="replaceable"><code>link_symbol</code></em></code></span></dt><dd><p>
This form of the <code class="literal">AS</code> 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 <em class="replaceable"><code>obj_file</code></em> is the name of the shared
library file containing the compiled C function, and is interpreted
as for the <a class="link" href="sql-load.html" title="LOAD"><code class="command">LOAD</code></a> command. The string
<em class="replaceable"><code>link_symbol</code></em> 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).
</p><p>
When repeated <code class="command">CREATE FUNCTION</code> 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.
</p></dd><dt><span class="term"><em class="replaceable"><code>sql_body</code></em></span></dt><dd><p>
The body of a <code class="literal">LANGUAGE SQL</code> function. This can
either be a single statement
</p><pre class="programlisting">
RETURN <em class="replaceable"><code>expression</code></em>
</pre><p>
or a block
</p><pre class="programlisting">
BEGIN ATOMIC
<em class="replaceable"><code>statement</code></em>;
<em class="replaceable"><code>statement</code></em>;
...
<em class="replaceable"><code>statement</code></em>;
END
</pre><p>
</p><p>
This is similar to writing the text of the function body as a string
constant (see <em class="replaceable"><code>definition</code></em> above), but there
are some differences: This form only works for <code class="literal">LANGUAGE
SQL</code>, 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 <code class="literal">DROP
... CASCADE</code> 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.
</p></dd></dl></div></div><div class="refsect1" id="SQL-CREATEFUNCTION-OVERLOADING"><h2>Overloading</h2><p>
<span class="productname">PostgreSQL</span> allows function
<em class="firstterm">overloading</em>; 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 <a class="xref" href="typeconv-func.html" title="10.3. Functions">Section 10.3</a>.
</p><p>
Two functions are considered the same if they have the same names and
<span class="emphasis"><em>input</em></span> argument types, ignoring any <code class="literal">OUT</code>
parameters. Thus for example these declarations conflict:
</p><pre class="programlisting">
CREATE FUNCTION foo(int) ...
CREATE FUNCTION foo(int, out text) ...
</pre><p>
</p><p>
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
</p><pre class="programlisting">
CREATE FUNCTION foo(int) ...
CREATE FUNCTION foo(int, int default 42) ...
</pre><p>
A call <code class="literal">foo(10)</code> will fail due to the ambiguity about which
function should be called.
</p></div><div class="refsect1" id="SQL-CREATEFUNCTION-NOTES"><h2>Notes</h2><p>
The full <acronym class="acronym">SQL</acronym> type syntax is allowed for
declaring a function's arguments and return value. However,
parenthesized type modifiers (e.g., the precision field for
type <code class="type">numeric</code>) are discarded by <code class="command">CREATE FUNCTION</code>.
Thus for example
<code class="literal">CREATE FUNCTION foo (varchar(10)) ...</code>
is exactly the same as
<code class="literal">CREATE FUNCTION foo (varchar) ...</code>.
</p><p>
When replacing an existing function with <code class="command">CREATE OR REPLACE
FUNCTION</code>, 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.
</p><p>
If a function is declared <code class="literal">STRICT</code> with a <code class="literal">VARIADIC</code>
argument, the strictness check tests that the variadic array <span class="emphasis"><em>as
a whole</em></span> is non-null. The function will still be called if the
array has null elements.
</p></div><div class="refsect1" id="SQL-CREATEFUNCTION-EXAMPLES"><h2>Examples</h2><p>
Add two integers using an SQL function:
</p><pre class="programlisting">
CREATE FUNCTION add(integer, integer) RETURNS integer
AS 'select $1 + $2;'
LANGUAGE SQL
IMMUTABLE
RETURNS NULL ON NULL INPUT;
</pre><p>
The same function written in a more SQL-conforming style, using argument
names and an unquoted body:
</p><pre class="programlisting">
CREATE FUNCTION add(a integer, b integer) RETURNS integer
LANGUAGE SQL
IMMUTABLE
RETURNS NULL ON NULL INPUT
RETURN a + b;
</pre><p>
</p><p>
Increment an integer, making use of an argument name, in
<span class="application">PL/pgSQL</span>:
</p><pre class="programlisting">
CREATE OR REPLACE FUNCTION increment(i integer) RETURNS integer AS $$
BEGIN
RETURN i + 1;
END;
$$ LANGUAGE plpgsql;
</pre><p>
</p><p>
Return a record containing multiple output parameters:
</p><pre class="programlisting">
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);
</pre><p>
You can do the same thing more verbosely with an explicitly named
composite type:
</p><pre class="programlisting">
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);
</pre><p>
Another way to return multiple columns is to use a <code class="literal">TABLE</code>
function:
</p><pre class="programlisting">
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);
</pre><p>
However, a <code class="literal">TABLE</code> function is different from the
preceding examples, because it actually returns a <span class="emphasis"><em>set</em></span>
of records, not just one record.
</p></div><div class="refsect1" id="SQL-CREATEFUNCTION-SECURITY"><h2>Writing <code class="literal">SECURITY DEFINER</code> Functions Safely</h2><a id="id-1.9.3.67.10.2" class="indexterm"></a><p>
Because a <code class="literal">SECURITY DEFINER</code> 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,
<a class="xref" href="runtime-config-client.html#GUC-SEARCH-PATH">search_path</a> 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 <code class="literal">pg_temp</code><a id="id-1.9.3.67.10.3.4" class="indexterm"></a> as the last entry in <code class="varname">search_path</code>.
This function illustrates safe usage:
</p><pre class="programlisting">
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;
</pre><p>
This function's intention is to access a table <code class="literal">admin.pwds</code>.
But without the <code class="literal">SET</code> clause, or with a <code class="literal">SET</code> clause
mentioning only <code class="literal">admin</code>, the function could be subverted by
creating a temporary table named <code class="literal">pwds</code>.
</p><p>
Before <span class="productname">PostgreSQL</span> version 8.3, the
<code class="literal">SET</code> clause was not available, and so older functions may
contain rather complicated logic to save, set, and restore
<code class="varname">search_path</code>. The <code class="literal">SET</code> clause is far easier
to use for this purpose.
</p><p>
Another point to keep in mind is that by default, execute privilege
is granted to <code class="literal">PUBLIC</code> for newly created functions
(see <a class="xref" href="ddl-priv.html" title="5.7. Privileges">Section 5.7</a> 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 <code class="literal">PUBLIC</code> 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:
</p><pre class="programlisting">
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;
</pre></div><div class="refsect1" id="SQL-CREATEFUNCTION-COMPAT"><h2>Compatibility</h2><p>
A <code class="command">CREATE FUNCTION</code> command is defined in the SQL
standard. The <span class="productname">PostgreSQL</span> 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 <span class="productname">PostgreSQL</span>.
</p><p>
The following are important compatibility issues:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
<code class="literal">OR REPLACE</code> is a PostgreSQL extension.
</p></li><li class="listitem"><p>
For compatibility with some other database systems, <em class="replaceable"><code>argmode</code></em> can be written either before or
after <em class="replaceable"><code>argname</code></em>. But only
the first way is standard-compliant.
</p></li><li class="listitem"><p>
For parameter defaults, the SQL standard specifies only the syntax with
the <code class="literal">DEFAULT</code> key word. The syntax with
<code class="literal">=</code> is used in T-SQL and Firebird.
</p></li><li class="listitem"><p>
The <code class="literal">SETOF</code> modifier is a PostgreSQL extension.
</p></li><li class="listitem"><p>
Only <code class="literal">SQL</code> is standardized as a language.
</p></li><li class="listitem"><p>
All other attributes except <code class="literal">CALLED ON NULL INPUT</code> and
<code class="literal">RETURNS NULL ON NULL INPUT</code> are not standardized.
</p></li><li class="listitem"><p>
For the body of <code class="literal">LANGUAGE SQL</code> functions, the SQL
standard only specifies the <em class="replaceable"><code>sql_body</code></em> form.
</p></li></ul></div><p>
</p><p>
Simple <code class="literal">LANGUAGE SQL</code> 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.
</p></div><div class="refsect1" id="id-1.9.3.67.12"><h2>See Also</h2><span class="simplelist"><a class="xref" href="sql-alterfunction.html" title="ALTER FUNCTION"><span class="refentrytitle">ALTER FUNCTION</span></a>, <a class="xref" href="sql-dropfunction.html" title="DROP FUNCTION"><span class="refentrytitle">DROP FUNCTION</span></a>, <a class="xref" href="sql-grant.html" title="GRANT"><span class="refentrytitle">GRANT</span></a>, <a class="xref" href="sql-load.html" title="LOAD"><span class="refentrytitle">LOAD</span></a>, <a class="xref" href="sql-revoke.html" title="REVOKE"><span class="refentrytitle">REVOKE</span></a></span></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="sql-createforeigntable.html" title="CREATE FOREIGN TABLE">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="sql-commands.html" title="SQL Commands">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="sql-creategroup.html" title="CREATE GROUP">Next</a></td></tr><tr><td width="40%" align="left" valign="top">CREATE FOREIGN TABLE </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.6 Documentation">Home</a></td><td width="40%" align="right" valign="top"> CREATE GROUP</td></tr></table></div></body></html>
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