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doc/src/sgml/ref/create_function.sgml
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<refentry id="SQL-CREATEFUNCTION">
<refmeta>
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<refentrytitle>CREATE FUNCTION</refentrytitle>
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<manvolnum>7</manvolnum>
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<refmiscinfo>SQL - Language Statements</refmiscinfo>
</refmeta>
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<refnamediv>
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<refname>CREATE FUNCTION</refname>
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<refpurpose>define a new function</refpurpose>
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</refnamediv>
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<indexterm zone="sql-createfunction">
<primary>CREATE FUNCTION</primary>
</indexterm>
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<refsynopsisdiv>
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<synopsis>
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CREATE [ OR REPLACE ] FUNCTION
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<replaceable class="parameter">name</replaceable> ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [ { DEFAULT | = } <replaceable class="parameter">default_expr</replaceable> ] [, ...] ] )
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[ RETURNS <replaceable class="parameter">rettype</replaceable>
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| RETURNS TABLE ( <replaceable class="parameter">column_name</replaceable> <replaceable class="parameter">column_type</replaceable> [, ...] ) ]
{ LANGUAGE <replaceable class="parameter">lang_name</replaceable>
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| WINDOW
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| IMMUTABLE | STABLE | VOLATILE | [ NOT ] LEAKPROOF
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| CALLED ON NULL INPUT | RETURNS NULL ON NULL INPUT | STRICT
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| [ EXTERNAL ] SECURITY INVOKER | [ EXTERNAL ] SECURITY DEFINER
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| COST <replaceable class="parameter">execution_cost</replaceable>
| ROWS <replaceable class="parameter">result_rows</replaceable>
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| SET <replaceable class="parameter">configuration_parameter</replaceable> { TO <replaceable class="parameter">value</replaceable> | = <replaceable class="parameter">value</replaceable> | FROM CURRENT }
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| AS '<replaceable class="parameter">definition</replaceable>'
| AS '<replaceable class="parameter">obj_file</replaceable>', '<replaceable class="parameter">link_symbol</replaceable>'
} ...
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[ WITH ( <replaceable class="parameter">attribute</replaceable> [, ...] ) ]
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</synopsis>
</refsynopsisdiv>
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<refsect1 id="sql-createfunction-description">
<title>Description</title>
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<para>
<command>CREATE FUNCTION</command> defines a new function.
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<command>CREATE OR REPLACE FUNCTION</command> will either create a
new function, or replace an existing definition.
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To be able to define a function, the user must have the
<literal>USAGE</literal> privilege on the language.
</para>
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<para>
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
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with the same input argument types in the same schema. However,
Update reference documentation on may/can/might:
Standard English uses "may", "can", and "might" in different ways:
may - permission, "You may borrow my rake."
can - ability, "I can lift that log."
might - possibility, "It might rain today."
Unfortunately, in conversational English, their use is often mixed, as
in, "You may use this variable to do X", when in fact, "can" is a better
choice. Similarly, "It may crash" is better stated, "It might crash".
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functions of different argument types can share a name (this is
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called <firstterm>overloading</>).
</para>
<para>
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To replace the current definition of an existing function, use
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<command>CREATE OR REPLACE FUNCTION</command>. It is not possible
to change the name or argument types of a function this way (if you
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tried, you would actually be creating a new, distinct function).
Also, <command>CREATE OR REPLACE FUNCTION</command> will not let
you change the return type of an existing function. To do that,
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you must drop and recreate the function. (When using <literal>OUT</>
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parameters, that means you cannot change the types of any
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<literal>OUT</> parameters except by dropping the function.)
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</para>
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<para>
When <command>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 command. You must own the function
to replace it (this includes being a member of the owning role).
</para>
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<para>
If you drop and then recreate a function, the new function is not
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the same entity as the old; you will have to drop existing rules, views,
triggers, etc. that refer to the old function. Use
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<command>CREATE OR REPLACE FUNCTION</command> to change a function
definition without breaking objects that refer to the function.
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Also, <command>ALTER FUNCTION</> can be used to change most of the
auxiliary properties of an existing function.
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</para>
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<para>
The user that creates the function becomes the owner of the function.
</para>
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<para>
To be able to create a function, you must have <literal>USAGE</literal>
privilege on the argument types and the return type.
</para>
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</refsect1>
<refsect1>
<title>Parameters</title>
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<variablelist>
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<varlistentry>
<term><replaceable class="parameter">name</replaceable></term>
<listitem>
<para>
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The name (optionally schema-qualified) of the function to create.
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</para>
</listitem>
</varlistentry>
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<varlistentry>
<term><replaceable class="parameter">argmode</replaceable></term>
<listitem>
<para>
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The mode of an argument: <literal>IN</>, <literal>OUT</>,
<literal>INOUT</>, or <literal>VARIADIC</>.
If omitted, the default is <literal>IN</>.
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Only <literal>OUT</> arguments can follow a <literal>VARIADIC</> one.
Also, <literal>OUT</> and <literal>INOUT</> arguments cannot be used
together with the <literal>RETURNS TABLE</> notation.
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</para>
</listitem>
</varlistentry>
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<varlistentry>
<term><replaceable class="parameter">argname</replaceable></term>
<listitem>
<para>
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The name of an argument. Some languages (including SQL and PL/pgSQL)
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let you use the name in the function body. For other languages the
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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 <xref
linkend="sql-syntax-calling-funcs">). In any case, the name
of an output argument is significant, because it defines the column
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name in the result row type. (If you omit the name for an output
argument, the system will choose a default column name.)
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</para>
</listitem>
</varlistentry>
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<varlistentry>
<term><replaceable class="parameter">argtype</replaceable></term>
<listitem>
<para>
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The data type(s) of the function's arguments (optionally
Update reference documentation on may/can/might:
Standard English uses "may", "can", and "might" in different ways:
may - permission, "You may borrow my rake."
can - ability, "I can lift that log."
might - possibility, "It might rain today."
Unfortunately, in conversational English, their use is often mixed, as
in, "You may use this variable to do X", when in fact, "can" is a better
choice. Similarly, "It may crash" is better stated, "It might crash".
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schema-qualified), if any. The argument types can be base, composite,
or domain types, or can reference the type of a table column.
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</para>
<para>
Update reference documentation on may/can/might:
Standard English uses "may", "can", and "might" in different ways:
may - permission, "You may borrow my rake."
can - ability, "I can lift that log."
might - possibility, "It might rain today."
Unfortunately, in conversational English, their use is often mixed, as
in, "You may use this variable to do X", when in fact, "can" is a better
choice. Similarly, "It may crash" is better stated, "It might crash".
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Depending on the implementation language it might also be allowed
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to specify <quote>pseudotypes</> such as <type>cstring</>.
Pseudotypes indicate that the actual argument type is either
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incompletely specified, or outside the set of ordinary SQL data types.
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</para>
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<para>
The type of a column is referenced by writing
<literal><replaceable
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class="parameter">table_name</replaceable>.<replaceable
class="parameter">column_name</replaceable>%TYPE</literal>.
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Using this feature can sometimes help make a function independent of
changes to the definition of a table.
</para>
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</listitem>
</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">default_expr</replaceable></term>
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<listitem>
<para>
An expression to be used as default value if the parameter is
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not specified. The expression has to be coercible to the
argument type of the parameter.
Only input (including <literal>INOUT</>) parameters can have a default
value. All input parameters following a
parameter with a default value must have default values as well.
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</para>
</listitem>
</varlistentry>
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<varlistentry>
<term><replaceable class="parameter">rettype</replaceable></term>
<listitem>
<para>
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The return data type (optionally schema-qualified). The return type
Update reference documentation on may/can/might:
Standard English uses "may", "can", and "might" in different ways:
may - permission, "You may borrow my rake."
can - ability, "I can lift that log."
might - possibility, "It might rain today."
Unfortunately, in conversational English, their use is often mixed, as
in, "You may use this variable to do X", when in fact, "can" is a better
choice. Similarly, "It may crash" is better stated, "It might crash".
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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
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to specify <quote>pseudotypes</> such as <type>cstring</>.
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If the function is not supposed to return a value, specify
<type>void</> as the return type.
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</para>
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<para>
When there are <literal>OUT</> or <literal>INOUT</> parameters,
Update reference documentation on may/can/might:
Standard English uses "may", "can", and "might" in different ways:
may - permission, "You may borrow my rake."
can - ability, "I can lift that log."
might - possibility, "It might rain today."
Unfortunately, in conversational English, their use is often mixed, as
in, "You may use this variable to do X", when in fact, "can" is a better
choice. Similarly, "It may crash" is better stated, "It might crash".
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the <literal>RETURNS</> clause can be omitted. If present, it
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must agree with the result type implied by the output parameters:
<literal>RECORD</> if there are multiple output parameters, or
the same type as the single output parameter.
</para>
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<para>
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The <literal>SETOF</literal>
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modifier indicates that the function will return a set of
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items, rather than a single item.
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</para>
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<para>
The type of a column is referenced by writing
<literal><replaceable
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class="parameter">table_name</replaceable>.<replaceable
class="parameter">column_name</replaceable>%TYPE</literal>.
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</para>
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</listitem>
</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">column_name</replaceable></term>
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<listitem>
<para>
The name of an output column in the <literal>RETURNS TABLE</>
syntax. This is effectively another way of declaring a named
<literal>OUT</> parameter, except that <literal>RETURNS TABLE</>
also implies <literal>RETURNS SETOF</>.
</para>
</listitem>
</varlistentry>
<varlistentry>
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<term><replaceable class="parameter">column_type</replaceable></term>
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<listitem>
<para>
The data type of an output column in the <literal>RETURNS TABLE</>
syntax.
</para>
</listitem>
</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">lang_name</replaceable></term>
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<listitem>
<para>
The name of the language that the function is implemented in.
Update reference documentation on may/can/might:
Standard English uses "may", "can", and "might" in different ways:
may - permission, "You may borrow my rake."
can - ability, "I can lift that log."
might - possibility, "It might rain today."
Unfortunately, in conversational English, their use is often mixed, as
in, "You may use this variable to do X", when in fact, "can" is a better
choice. Similarly, "It may crash" is better stated, "It might crash".
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Can be <literal>SQL</literal>, <literal>C</literal>,
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<literal>internal</literal>, or the name of a user-defined
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procedural language. For backward compatibility,
Update reference documentation on may/can/might:
Standard English uses "may", "can", and "might" in different ways:
may - permission, "You may borrow my rake."
can - ability, "I can lift that log."
might - possibility, "It might rain today."
Unfortunately, in conversational English, their use is often mixed, as
in, "You may use this variable to do X", when in fact, "can" is a better
choice. Similarly, "It may crash" is better stated, "It might crash".
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the name can be enclosed by single quotes.
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</para>
</listitem>
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</varlistentry>
<varlistentry>
<term><literal>WINDOW</literal></term>
<listitem>
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<para><literal>WINDOW</literal> indicates that the function is a
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<firstterm>window function</> rather than a plain function.
This is currently only useful for functions written in C.
The <literal>WINDOW</> attribute cannot be changed when
replacing an existing function definition.
</para>
</listitem>
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</varlistentry>
<varlistentry>
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<term><literal>IMMUTABLE</literal></term>
<term><literal>STABLE</literal></term>
<term><literal>VOLATILE</literal></term>
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<listitem>
<para>
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These attributes inform the query optimizer about the behavior
of the function. At most one choice
Update reference documentation on may/can/might:
Standard English uses "may", "can", and "might" in different ways:
may - permission, "You may borrow my rake."
can - ability, "I can lift that log."
might - possibility, "It might rain today."
Unfortunately, in conversational English, their use is often mixed, as
in, "You may use this variable to do X", when in fact, "can" is a better
choice. Similarly, "It may crash" is better stated, "It might crash".
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can be specified. If none of these appear,
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<literal>VOLATILE</literal> is the default assumption.
</para>
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<para><literal>IMMUTABLE</literal> indicates that the function
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cannot modify the database and always
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returns the same result when given the same argument values; that
is, it does not do database lookups or otherwise use information not
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directly present in its argument list. If this option is given,
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any call of the function with all-constant arguments can be
immediately replaced with the function value.
</para>
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<para><literal>STABLE</literal> indicates that the function
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cannot modify the database,
and that within a single table scan it will consistently
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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,
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parameter variables (such as the current time zone), etc. (It is
inappropriate for <literal>AFTER</> triggers that wish to
query rows modified by the current command.) Also note
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that the <function>current_timestamp</> family of functions qualify
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as stable, since their values do not change within a transaction.
</para>
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<para><literal>VOLATILE</literal> indicates that the function value can
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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 <literal>random()</>, <literal>currval()</>,
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<literal>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
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<literal>setval()</>.
</para>
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<para>
For additional details see <xref linkend="xfunc-volatility">.
</para>
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</listitem>
</varlistentry>
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<varlistentry>
<term><literal>LEAKPROOF</literal></term>
<listitem>
<para>
<literal>LEAKPROOF</literal> 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
<literal>security_barrier</literal> option. See
<xref linkend="sql-createview"> and <xref linkend="rules-privileges">.
This option can only be set by the superuser.
</para>
</listitem>
</varlistentry>
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<varlistentry>
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<term><literal>CALLED ON NULL INPUT</literal></term>
<term><literal>RETURNS NULL ON NULL INPUT</literal></term>
<term><literal>STRICT</literal></term>
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<listitem>
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<para><literal>CALLED ON NULL INPUT</literal> (the default) indicates
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that the function will be called normally when some of its
arguments are null. It is then the function author's
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responsibility to check for null values if necessary and respond
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appropriately.
</para>
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<para><literal>RETURNS NULL ON NULL INPUT</literal> or
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<literal>STRICT</literal> indicates that the function always
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returns null whenever any of its arguments are null. If this
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parameter is specified, the function is not executed when there
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are null arguments; instead a null result is assumed
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automatically.
</para>
</listitem>
</varlistentry>
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<varlistentry>
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<term><literal><optional>EXTERNAL</optional> SECURITY INVOKER</literal></term>
<term><literal><optional>EXTERNAL</optional> SECURITY DEFINER</literal></term>
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<listitem>
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<para><literal>SECURITY INVOKER</literal> indicates that the function
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is to be executed with the privileges of the user that calls it.
That is the default. <literal>SECURITY DEFINER</literal>
specifies that the function is to be executed with the
privileges of the user that created it.
</para>
<para>
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The key word <literal>EXTERNAL</literal> is allowed for SQL
conformance, but it is optional since, unlike in SQL, this feature
applies to all functions not only external ones.
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</para>
</listitem>
</varlistentry>
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<varlistentry>
<term><replaceable class="parameter">execution_cost</replaceable></term>
<listitem>
<para>
A positive number giving the estimated execution cost for the function,
in units of <xref linkend="guc-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.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">result_rows</replaceable></term>
<listitem>
<para>
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.
</para>
</listitem>
</varlistentry>
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<varlistentry>
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<term><replaceable>configuration_parameter</replaceable></term>
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<term><replaceable>value</replaceable></term>
<listitem>
<para>
The <literal>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.
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<literal>SET FROM CURRENT</> saves the session's current value of
the parameter as the value to be applied when the function is entered.
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</para>
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<para>
If a <literal>SET</> clause is attached to a function, then
the effects of a <command>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
<command>SET</> command (without <literal>LOCAL</>) overrides the
<literal>SET</> clause, much as it would do for a previous <command>SET
LOCAL</> command: the effects of such a command will persist after
function exit, unless the current transaction is rolled back.
</para>
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<para>
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See <xref linkend="sql-set"> and
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<xref linkend="runtime-config">
for more information about allowed parameter names and values.
</para>
</listitem>
</varlistentry>
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<varlistentry>
<term><replaceable class="parameter">definition</replaceable></term>
<listitem>
<para>
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A string constant defining the function; the meaning depends on the
Update reference documentation on may/can/might:
Standard English uses "may", "can", and "might" in different ways:
may - permission, "You may borrow my rake."
can - ability, "I can lift that log."
might - possibility, "It might rain today."
Unfortunately, in conversational English, their use is often mixed, as
in, "You may use this variable to do X", when in fact, "can" is a better
choice. Similarly, "It may crash" is better stated, "It might crash".
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language. It can be an internal function name, the path to an
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object file, an SQL command, or text in a procedural language.
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</para>
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<para>
It is often helpful to use dollar quoting (see <xref
linkend="sql-syntax-dollar-quoting">) 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.
</para>
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</listitem>
</varlistentry>
<varlistentry>
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<term><literal><replaceable class="parameter">obj_file</replaceable>, <replaceable class="parameter">link_symbol</replaceable></literal></term>
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<listitem>
<para>
This form of the <literal>AS</literal> clause is used for
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dynamically loadable C language functions when the function name
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in the C language source code is not the same as the name of
the SQL function. The string <replaceable
class="parameter">obj_file</replaceable> is the name of the
file containing the dynamically loadable object, and
<replaceable class="parameter">link_symbol</replaceable> is the
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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.
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</para>
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<para>
When repeated <command>CREATE FUNCTION</command> 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.
</para>
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</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">attribute</replaceable></term>
<listitem>
<para>
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The historical way to specify optional pieces of information
Update reference documentation on may/can/might:
Standard English uses "may", "can", and "might" in different ways:
may - permission, "You may borrow my rake."
can - ability, "I can lift that log."
might - possibility, "It might rain today."
Unfortunately, in conversational English, their use is often mixed, as
in, "You may use this variable to do X", when in fact, "can" is a better
choice. Similarly, "It may crash" is better stated, "It might crash".
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about the function. The following attributes can appear here:
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<variablelist>
<varlistentry>
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<term><literal>isStrict</></term>
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<listitem>
<para>
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Equivalent to <literal>STRICT</literal> or <literal>RETURNS NULL ON NULL INPUT</literal>.
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</para>
</listitem>
</varlistentry>
<varlistentry>
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<term><literal>isCachable</></term>
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<listitem>
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<para><literal>isCachable</literal> is an obsolete equivalent of
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<literal>IMMUTABLE</literal>; it's still accepted for
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backwards-compatibility reasons.
</para>
</listitem>
</varlistentry>
</variablelist>
Attribute names are not case-sensitive.
</para>
</listitem>
</varlistentry>
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</variablelist>
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<para>
Refer to <xref linkend="xfunc"> for further information on writing
functions.
</para>
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</refsect1>
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<refsect1 id="sql-createfunction-overloading">
<title>Overloading</title>
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<para>
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<productname>PostgreSQL</productname> allows function
<firstterm>overloading</firstterm>; that is, the same name can be
used for several different functions so long as they have distinct
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input argument types. However, the C names of all functions must be
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different, so you must give overloaded C functions different C
names (for example, use the argument types as part of the C
names).
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</para>
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<para>
Two functions are considered the same if they have the same names and
<emphasis>input</> argument types, ignoring any <literal>OUT</>
parameters. Thus for example these declarations conflict:
<programlisting>
CREATE FUNCTION foo(int) ...
CREATE FUNCTION foo(int, out text) ...
</programlisting>
</para>
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<para>
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
<programlisting>
CREATE FUNCTION foo(int) ...
CREATE FUNCTION foo(int, int default 42) ...
</programlisting>
A call <literal>foo(10)</> will fail due to the ambiguity about which
function should be called.
</para>
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</refsect1>
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<refsect1 id="sql-createfunction-notes">
<title>Notes</title>
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<para>
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The full <acronym>SQL</acronym> type syntax is allowed for
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declaring a function's arguments and return value. However,
parenthesized type modifiers (e.g., the precision field for
type <type>numeric</type>) are discarded by <command>CREATE FUNCTION</>.
Thus for example
<literal>CREATE FUNCTION foo (varchar(10)) ...</>
is exactly the same as
<literal>CREATE FUNCTION foo (varchar) ...</>.
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</para>
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<para>
When replacing an existing function with <command>CREATE OR REPLACE
FUNCTION</>, 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.
</para>
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<para>
If a function is declared <literal>STRICT</> with a <literal>VARIADIC</>
argument, the strictness check tests that the variadic array <emphasis>as
a whole</> is non-null. The function will still be called if the
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array has null elements.
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</para>
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</refsect1>
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<refsect1 id="sql-createfunction-examples">
<title>Examples</title>
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<para>
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Here are some trivial examples to help you get started. For more
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information and examples, see <xref linkend="xfunc">.
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<programlisting>
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CREATE FUNCTION add(integer, integer) RETURNS integer
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AS 'select $1 + $2;'
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LANGUAGE SQL
IMMUTABLE
RETURNS NULL ON NULL INPUT;
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</programlisting>
</para>
<para>
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Increment an integer, making use of an argument name, in
<application>PL/pgSQL</application>:
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<programlisting>
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CREATE OR REPLACE FUNCTION increment(i integer) RETURNS integer AS $$
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BEGIN
RETURN i + 1;
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END;
$$ LANGUAGE plpgsql;
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</programlisting>
</para>
<para>
Return a record containing multiple output parameters:
<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);
</programlisting>
You can do the same thing more verbosely with an explicitly named
composite type:
<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);
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</programlisting>
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Another way to return multiple columns is to use a <literal>TABLE</>
function:
<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);
</programlisting>
However, a <literal>TABLE</> function is different from the
preceding examples, because it actually returns a <emphasis>set</>
of records, not just one record.
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</para>
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</refsect1>
2001-05-19 11:01:10 +02:00
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<refsect1 id="sql-createfunction-security">
<title>Writing <literal>SECURITY DEFINER</literal> Functions Safely</title>
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<indexterm>
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<primary><varname>search_path</varname> configuration parameter</>
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<secondary>use in securing functions</>
</indexterm>
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<para>
Because a <literal>SECURITY DEFINER</literal> 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,
<xref linkend="guc-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
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function. Particularly important in this regard is the
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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,
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write <literal>pg_temp</><indexterm><primary>pg_temp</><secondary>securing functions</></> as the last entry in <varname>search_path</>.
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This function illustrates safe usage:
</para>
<programlisting>
CREATE FUNCTION check_password(uname TEXT, pass TEXT)
RETURNS BOOLEAN AS $$
DECLARE passed BOOLEAN;
BEGIN
SELECT (pwd = $2) INTO passed
FROM pwds
WHERE username = $1;
RETURN passed;
END;
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$$ LANGUAGE plpgsql
SECURITY DEFINER
-- Set a secure search_path: trusted schema(s), then 'pg_temp'.
SET search_path = admin, pg_temp;
</programlisting>
<para>
Before <productname>PostgreSQL</productname> version 8.3, the
<literal>SET</> option was not available, and so older functions may
contain rather complicated logic to save, set, and restore
<varname>search_path</>. The <literal>SET</> option is far easier
to use for this purpose.
</para>
<para>
Another point to keep in mind is that by default, execute privilege
is granted to <literal>PUBLIC</> for newly created functions
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(see <xref linkend="sql-grant"> for more
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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 <literal>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:
</para>
<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;
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</programlisting>
</refsect1>
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<refsect1 id="sql-createfunction-compat">
<title>Compatibility</title>
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<para>
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A <command>CREATE FUNCTION</command> command is defined in SQL:1999 and later.
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The <productname>PostgreSQL</productname> version is similar but
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not fully compatible. The attributes are not portable, neither are the
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different available languages.
</para>
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<para>
For compatibility with some other database systems,
<replaceable class="parameter">argmode</replaceable> can be written
either before or after <replaceable class="parameter">argname</replaceable>.
But only the first way is standard-compliant.
</para>
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<para>
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For parameter defaults, the SQL standard specifies only the syntax with
the <literal>DEFAULT</literal> key word. The syntax
with <literal>=</literal> is used in T-SQL and Firebird.
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</para>
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</refsect1>
1998-09-16 16:43:12 +02:00
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2005-01-04 01:39:53 +01:00
<refsect1>
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<title>See Also</title>
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<simplelist type="inline">
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<member><xref linkend="sql-alterfunction"></member>
<member><xref linkend="sql-dropfunction"></member>
<member><xref linkend="sql-grant"></member>
<member><xref linkend="sql-load"></member>
<member><xref linkend="sql-revoke"></member>
<member><xref linkend="app-createlang"></member>
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</simplelist>
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</refsect1>
2001-05-19 11:01:10 +02:00
1999-06-14 09:37:05 +02:00
</refentry>