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><H1
><A
NAME="SQL-CREATEFUNCTION"
></A
>CREATE FUNCTION</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN68476"
></A
><H2
>Name</H2
>CREATE FUNCTION -- define a new function</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN68481"
></A
><H2
>Synopsis</H2
><PRE
CLASS="SYNOPSIS"
>CREATE [ OR REPLACE ] FUNCTION
<TT
CLASS="REPLACEABLE"
><I
>name</I
></TT
> ( [ [ <TT
CLASS="REPLACEABLE"
><I
>argmode</I
></TT
> ] [ <TT
CLASS="REPLACEABLE"
><I
>argname</I
></TT
> ] <TT
CLASS="REPLACEABLE"
><I
>argtype</I
></TT
> [ { DEFAULT | = } <TT
CLASS="REPLACEABLE"
><I
>default_expr</I
></TT
> ] [, ...] ] )
[ RETURNS <TT
CLASS="REPLACEABLE"
><I
>rettype</I
></TT
>
| RETURNS TABLE ( <TT
CLASS="REPLACEABLE"
><I
>column_name</I
></TT
> <TT
CLASS="REPLACEABLE"
><I
>column_type</I
></TT
> [, ...] ) ]
{ LANGUAGE <TT
CLASS="REPLACEABLE"
><I
>lang_name</I
></TT
>
| WINDOW
| IMMUTABLE | STABLE | VOLATILE | [ NOT ] LEAKPROOF
| CALLED ON NULL INPUT | RETURNS NULL ON NULL INPUT | STRICT
| [ EXTERNAL ] SECURITY INVOKER | [ EXTERNAL ] SECURITY DEFINER
| COST <TT
CLASS="REPLACEABLE"
><I
>execution_cost</I
></TT
>
| ROWS <TT
CLASS="REPLACEABLE"
><I
>result_rows</I
></TT
>
| SET <TT
CLASS="REPLACEABLE"
><I
>configuration_parameter</I
></TT
> { TO <TT
CLASS="REPLACEABLE"
><I
>value</I
></TT
> | = <TT
CLASS="REPLACEABLE"
><I
>value</I
></TT
> | FROM CURRENT }
| AS '<TT
CLASS="REPLACEABLE"
><I
>definition</I
></TT
>'
| AS '<TT
CLASS="REPLACEABLE"
><I
>obj_file</I
></TT
>', '<TT
CLASS="REPLACEABLE"
><I
>link_symbol</I
></TT
>'
} ...
[ WITH ( <TT
CLASS="REPLACEABLE"
><I
>attribute</I
></TT
> [, ...] ) ]</PRE
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="SQL-CREATEFUNCTION-DESCRIPTION"
></A
><H2
>Description</H2
><P
> <TT
CLASS="COMMAND"
>CREATE FUNCTION</TT
> defines a new function.
<TT
CLASS="COMMAND"
>CREATE OR REPLACE FUNCTION</TT
> will either create a
new function, or replace an existing definition.
To be able to define a function, the user must have the
<TT
CLASS="LITERAL"
>USAGE</TT
> 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
with the same input argument types in the same schema. However,
functions of different argument types can share a name (this is
called <I
CLASS="FIRSTTERM"
>overloading</I
>).
</P
><P
> To replace the current definition of an existing function, use
<TT
CLASS="COMMAND"
>CREATE OR REPLACE FUNCTION</TT
>. 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, <TT
CLASS="COMMAND"
>CREATE OR REPLACE FUNCTION</TT
> will not let
you change the return type of an existing function. To do that,
you must drop and recreate the function. (When using <TT
CLASS="LITERAL"
>OUT</TT
>
parameters, that means you cannot change the types of any
<TT
CLASS="LITERAL"
>OUT</TT
> parameters except by dropping the function.)
</P
><P
> When <TT
CLASS="COMMAND"
>CREATE OR REPLACE FUNCTION</TT
> 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
<TT
CLASS="COMMAND"
>CREATE OR REPLACE FUNCTION</TT
> to change a function
definition without breaking objects that refer to the function.
Also, <TT
CLASS="COMMAND"
>ALTER FUNCTION</TT
> 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 <TT
CLASS="LITERAL"
>USAGE</TT
>
privilege on the argument types and the return type.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN68522"
></A
><H2
>Parameters</H2
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="REPLACEABLE"
><I
>name</I
></TT
></DT
><DD
><P
> The name (optionally schema-qualified) of the function to create.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>argmode</I
></TT
></DT
><DD
><P
> The mode of an argument: <TT
CLASS="LITERAL"
>IN</TT
>, <TT
CLASS="LITERAL"
>OUT</TT
>,
<TT
CLASS="LITERAL"
>INOUT</TT
>, or <TT
CLASS="LITERAL"
>VARIADIC</TT
>.
If omitted, the default is <TT
CLASS="LITERAL"
>IN</TT
>.
Only <TT
CLASS="LITERAL"
>OUT</TT
> arguments can follow a <TT
CLASS="LITERAL"
>VARIADIC</TT
> one.
Also, <TT
CLASS="LITERAL"
>OUT</TT
> and <TT
CLASS="LITERAL"
>INOUT</TT
> arguments cannot be used
together with the <TT
CLASS="LITERAL"
>RETURNS TABLE</TT
> notation.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>argname</I
></TT
></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
HREF="sql-syntax-calling-funcs.html"
>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
><TT
CLASS="REPLACEABLE"
><I
>argtype</I
></TT
></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"
>"pseudotypes"</SPAN
> such as <TT
CLASS="TYPE"
>cstring</TT
>.
Pseudotypes 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
<TT
CLASS="LITERAL"
><TT
CLASS="REPLACEABLE"
><I
>table_name</I
></TT
>.<TT
CLASS="REPLACEABLE"
><I
>column_name</I
></TT
>%TYPE</TT
>.
Using this feature can sometimes help make a function independent of
changes to the definition of a table.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>default_expr</I
></TT
></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 <TT
CLASS="LITERAL"
>INOUT</TT
>) 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
><TT
CLASS="REPLACEABLE"
><I
>rettype</I
></TT
></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"
>"pseudotypes"</SPAN
> such as <TT
CLASS="TYPE"
>cstring</TT
>.
If the function is not supposed to return a value, specify
<TT
CLASS="TYPE"
>void</TT
> as the return type.
</P
><P
> When there are <TT
CLASS="LITERAL"
>OUT</TT
> or <TT
CLASS="LITERAL"
>INOUT</TT
> parameters,
the <TT
CLASS="LITERAL"
>RETURNS</TT
> clause can be omitted. If present, it
must agree with the result type implied by the output parameters:
<TT
CLASS="LITERAL"
>RECORD</TT
> if there are multiple output parameters, or
the same type as the single output parameter.
</P
><P
> The <TT
CLASS="LITERAL"
>SETOF</TT
>
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
<TT
CLASS="LITERAL"
><TT
CLASS="REPLACEABLE"
><I
>table_name</I
></TT
>.<TT
CLASS="REPLACEABLE"
><I
>column_name</I
></TT
>%TYPE</TT
>.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>column_name</I
></TT
></DT
><DD
><P
> The name of an output column in the <TT
CLASS="LITERAL"
>RETURNS TABLE</TT
>
syntax. This is effectively another way of declaring a named
<TT
CLASS="LITERAL"
>OUT</TT
> parameter, except that <TT
CLASS="LITERAL"
>RETURNS TABLE</TT
>
also implies <TT
CLASS="LITERAL"
>RETURNS SETOF</TT
>.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>column_type</I
></TT
></DT
><DD
><P
> The data type of an output column in the <TT
CLASS="LITERAL"
>RETURNS TABLE</TT
>
syntax.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>lang_name</I
></TT
></DT
><DD
><P
> The name of the language that the function is implemented in.
Can be <TT
CLASS="LITERAL"
>SQL</TT
>, <TT
CLASS="LITERAL"
>C</TT
>,
<TT
CLASS="LITERAL"
>internal</TT
>, or the name of a user-defined
procedural language. For backward compatibility,
the name can be enclosed by single quotes.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>WINDOW</TT
></DT
><DD
><P
><TT
CLASS="LITERAL"
>WINDOW</TT
> indicates that the function is a
<I
CLASS="FIRSTTERM"
>window function</I
> rather than a plain function.
This is currently only useful for functions written in C.
The <TT
CLASS="LITERAL"
>WINDOW</TT
> attribute cannot be changed when
replacing an existing function definition.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>IMMUTABLE</TT
><BR><TT
CLASS="LITERAL"
>STABLE</TT
><BR><TT
CLASS="LITERAL"
>VOLATILE</TT
></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,
<TT
CLASS="LITERAL"
>VOLATILE</TT
> is the default assumption.
</P
><P
><TT
CLASS="LITERAL"
>IMMUTABLE</TT
> 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
><TT
CLASS="LITERAL"
>STABLE</TT
> 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 <TT
CLASS="LITERAL"
>AFTER</TT
> 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
><TT
CLASS="LITERAL"
>VOLATILE</TT
> 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 <TT
CLASS="LITERAL"
>random()</TT
>, <TT
CLASS="LITERAL"
>currval()</TT
>,
<TT
CLASS="LITERAL"
>timeofday()</TT
>. 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
<TT
CLASS="LITERAL"
>setval()</TT
>.
</P
><P
> For additional details see <A
HREF="xfunc-volatility.html"
>Section 35.6</A
>.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>LEAKPROOF</TT
></DT
><DD
><P
> <TT
CLASS="LITERAL"
>LEAKPROOF</TT
> 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. The query planner may
push leakproof functions (but not others) into views created with the
<TT
CLASS="LITERAL"
>security_barrier</TT
> option. See
<A
HREF="sql-createview.html"
>CREATE VIEW</A
> and <A
HREF="rules-privileges.html"
>Section 37.4</A
>.
This option can only be set by the superuser.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>CALLED ON NULL INPUT</TT
><BR><TT
CLASS="LITERAL"
>RETURNS NULL ON NULL INPUT</TT
><BR><TT
CLASS="LITERAL"
>STRICT</TT
></DT
><DD
><P
><TT
CLASS="LITERAL"
>CALLED ON NULL INPUT</TT
> (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
><TT
CLASS="LITERAL"
>RETURNS NULL ON NULL INPUT</TT
> or
<TT
CLASS="LITERAL"
>STRICT</TT
> 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
><TT
CLASS="LITERAL"
>[<SPAN
CLASS="OPTIONAL"
>EXTERNAL</SPAN
>] SECURITY INVOKER</TT
><BR><TT
CLASS="LITERAL"
>[<SPAN
CLASS="OPTIONAL"
>EXTERNAL</SPAN
>] SECURITY DEFINER</TT
></DT
><DD
><P
><TT
CLASS="LITERAL"
>SECURITY INVOKER</TT
> indicates that the function
is to be executed with the privileges of the user that calls it.
That is the default. <TT
CLASS="LITERAL"
>SECURITY DEFINER</TT
>
specifies that the function is to be executed with the
privileges of the user that created it.
</P
><P
> The key word <TT
CLASS="LITERAL"
>EXTERNAL</TT
> 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
><TT
CLASS="REPLACEABLE"
><I
>execution_cost</I
></TT
></DT
><DD
><P
> A positive number giving the estimated execution cost for the function,
in units of <A
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
><TT
CLASS="REPLACEABLE"
><I
>result_rows</I
></TT
></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
><TT
CLASS="REPLACEABLE"
><I
>configuration_parameter</I
></TT
><BR><TT
CLASS="REPLACEABLE"
><I
>value</I
></TT
></DT
><DD
><P
> The <TT
CLASS="LITERAL"
>SET</TT
> 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.
<TT
CLASS="LITERAL"
>SET FROM CURRENT</TT
> saves the value of the parameter that
is current when <TT
CLASS="COMMAND"
>CREATE FUNCTION</TT
> is executed as the value
to be applied when the function is entered.
</P
><P
> If a <TT
CLASS="LITERAL"
>SET</TT
> clause is attached to a function, then
the effects of a <TT
CLASS="COMMAND"
>SET LOCAL</TT
> 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
<TT
CLASS="COMMAND"
>SET</TT
> command (without <TT
CLASS="LITERAL"
>LOCAL</TT
>) overrides the
<TT
CLASS="LITERAL"
>SET</TT
> clause, much as it would do for a previous <TT
CLASS="COMMAND"
>SET
LOCAL</TT
> command: the effects of such a command will persist after
function exit, unless the current transaction is rolled back.
</P
><P
> See <A
HREF="sql-set.html"
>SET</A
> and
<A
HREF="runtime-config.html"
>Chapter 18</A
>
for more information about allowed parameter names and values.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>definition</I
></TT
></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
HREF="sql-syntax-lexical.html#SQL-SYNTAX-DOLLAR-QUOTING"
>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
><TT
CLASS="LITERAL"
><TT
CLASS="REPLACEABLE"
><I
>obj_file</I
></TT
>, <TT
CLASS="REPLACEABLE"
><I
>link_symbol</I
></TT
></TT
></DT
><DD
><P
> This form of the <TT
CLASS="LITERAL"
>AS</TT
> 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 <TT
CLASS="REPLACEABLE"
><I
>obj_file</I
></TT
> is the name of the
file containing the dynamically loadable object, and
<TT
CLASS="REPLACEABLE"
><I
>link_symbol</I
></TT
> 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.
</P
><P
> When repeated <TT
CLASS="COMMAND"
>CREATE FUNCTION</TT
> 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
><TT
CLASS="REPLACEABLE"
><I
>attribute</I
></TT
></DT
><DD
><P
> The historical way to specify optional pieces of information
about the function. The following attributes can appear here:
<P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
>isStrict</TT
></DT
><DD
><P
> Equivalent to <TT
CLASS="LITERAL"
>STRICT</TT
> or <TT
CLASS="LITERAL"
>RETURNS NULL ON NULL INPUT</TT
>.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>isCachable</TT
></DT
><DD
><P
><TT
CLASS="LITERAL"
>isCachable</TT
> is an obsolete equivalent of
<TT
CLASS="LITERAL"
>IMMUTABLE</TT
>; it's still accepted for
backwards-compatibility reasons.
</P
></DD
></DL
></DIV
><P>
Attribute names are not case-sensitive.
</P
></DD
></DL
></DIV
><P
> Refer to <A
HREF="xfunc.html"
>Section 35.3</A
> for further information on writing
functions.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="SQL-CREATEFUNCTION-OVERLOADING"
></A
><H2
>Overloading</H2
><P
> <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> allows function
<I
CLASS="FIRSTTERM"
>overloading</I
>; 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).
</P
><P
> Two functions are considered the same if they have the same names and
<SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>input</I
></SPAN
> argument types, ignoring any <TT
CLASS="LITERAL"
>OUT</TT
>
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 <TT
CLASS="LITERAL"
>foo(10)</TT
> will fail due to the ambiguity about which
function should be called.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="SQL-CREATEFUNCTION-NOTES"
></A
><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 <TT
CLASS="TYPE"
>numeric</TT
>) are discarded by <TT
CLASS="COMMAND"
>CREATE FUNCTION</TT
>.
Thus for example
<TT
CLASS="LITERAL"
>CREATE FUNCTION foo (varchar(10)) ...</TT
>
is exactly the same as
<TT
CLASS="LITERAL"
>CREATE FUNCTION foo (varchar) ...</TT
>.
</P
><P
> When replacing an existing function with <TT
CLASS="COMMAND"
>CREATE OR REPLACE
FUNCTION</TT
>, 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 <TT
CLASS="LITERAL"
>STRICT</TT
> with a <TT
CLASS="LITERAL"
>VARIADIC</TT
>
argument, the strictness check tests that the variadic array <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>as
a whole</I
></SPAN
> is non-null. The function will still be called if the
array has null elements.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="SQL-CREATEFUNCTION-EXAMPLES"
></A
><H2
>Examples</H2
><P
> Here are some trivial examples to help you get started. For more
information and examples, see <A
HREF="xfunc.html"
>Section 35.3</A
>.
</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>
</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 <TT
CLASS="LITERAL"
>TABLE</TT
>
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 <TT
CLASS="LITERAL"
>TABLE</TT
> function is different from the
preceding examples, because it actually returns a <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>set</I
></SPAN
>
of records, not just one record.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="SQL-CREATEFUNCTION-SECURITY"
></A
><H2
>Writing <TT
CLASS="LITERAL"
>SECURITY DEFINER</TT
> Functions Safely</H2
><P
> Because a <TT
CLASS="LITERAL"
>SECURITY DEFINER</TT
> 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,
<A
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 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 <TT
CLASS="LITERAL"
>pg_temp</TT
> as the last entry in <TT
CLASS="VARNAME"
>search_path</TT
>.
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
> Before <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> version 8.3, the
<TT
CLASS="LITERAL"
>SET</TT
> option was not available, and so older functions may
contain rather complicated logic to save, set, and restore
<TT
CLASS="VARNAME"
>search_path</TT
>. The <TT
CLASS="LITERAL"
>SET</TT
> option 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 <TT
CLASS="LITERAL"
>PUBLIC</TT
> for newly created functions
(see <A
HREF="sql-grant.html"
>GRANT</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 <TT
CLASS="LITERAL"
>PUBLIC</TT
> 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"
><A
NAME="SQL-CREATEFUNCTION-COMPAT"
></A
><H2
>Compatibility</H2
><P
> A <TT
CLASS="COMMAND"
>CREATE FUNCTION</TT
> command is defined in SQL:1999 and later.
The <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> version is similar but
not fully compatible. The attributes are not portable, neither are the
different available languages.
</P
><P
> For compatibility with some other database systems,
<TT
CLASS="REPLACEABLE"
><I
>argmode</I
></TT
> can be written
either before or after <TT
CLASS="REPLACEABLE"
><I
>argname</I
></TT
>.
But only the first way is standard-compliant.
</P
><P
> The SQL standard does not specify parameter defaults. The syntax
with the <TT
CLASS="LITERAL"
>DEFAULT</TT
> 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 <TT
CLASS="LITERAL"
>=</TT
> is
used in T-SQL and Firebird.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN68821"
></A
><H2
>See Also</H2
><A
HREF="sql-alterfunction.html"
>ALTER FUNCTION</A
>, <A
HREF="sql-dropfunction.html"
>DROP FUNCTION</A
>, <A
HREF="sql-grant.html"
>GRANT</A
>, <A
HREF="sql-load.html"
>LOAD</A
>, <A
HREF="sql-revoke.html"
>REVOKE</A
>, <A
HREF="app-createlang.html"
><SPAN
CLASS="APPLICATION"
>createlang</SPAN
></A
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