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>Chapter 34. Extending <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
></TD
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><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="XFUNC-SQL"
>34.4. Query Language (<ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
>) Functions</A
></H1
><A
NAME="AEN40200"
></A
><P
> SQL functions execute an arbitrary list of SQL statements, returning
the result of the last query in the list.
In the simple (non-set)
case, the first row of the last query's result will be returned.
(Bear in mind that <SPAN
CLASS="QUOTE"
>"the first row"</SPAN
> of a multirow
result is not well-defined unless you use <TT
CLASS="LITERAL"
>ORDER BY</TT
>.)
If the last query happens
to return no rows at all, the null value will be returned.
</P
><P
> <A
NAME="AEN40208"
></A
> Alternatively,
an SQL function can be declared to return a set, by specifying the
function's return type as <TT
CLASS="LITERAL"
>SETOF
<TT
CLASS="REPLACEABLE"
><I
>sometype</I
></TT
></TT
>. In this case all rows of the
last query's result are returned. Further details appear below.
</P
><P
> The body of an SQL function must be a list of SQL
statements separated by semicolons. A semicolon after the last
statement is optional. Unless the function is declared to return
<TT
CLASS="TYPE"
>void</TT
>, the last statement must be a <TT
CLASS="COMMAND"
>SELECT</TT
>.
</P
><P
> Any collection of commands in the <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
>
language can be packaged together and defined as a function.
Besides <TT
CLASS="COMMAND"
>SELECT</TT
> queries, the commands can include data
modification queries (<TT
CLASS="COMMAND"
>INSERT</TT
>,
<TT
CLASS="COMMAND"
>UPDATE</TT
>, and <TT
CLASS="COMMAND"
>DELETE</TT
>), as well as
other SQL commands. (The only exception is that you cannot put
<TT
CLASS="COMMAND"
>BEGIN</TT
>, <TT
CLASS="COMMAND"
>COMMIT</TT
>, <TT
CLASS="COMMAND"
>ROLLBACK</TT
>, or
<TT
CLASS="COMMAND"
>SAVEPOINT</TT
> commands into a <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> function.)
However, the final command
must be a <TT
CLASS="COMMAND"
>SELECT</TT
> that returns whatever is
specified as the function's return type. Alternatively, if you
want to define a SQL function that performs actions but has no
useful value to return, you can define it as returning <TT
CLASS="TYPE"
>void</TT
>.
In that case, the function body must not end with a <TT
CLASS="COMMAND"
>SELECT</TT
>.
For example, this function removes rows with negative salaries from
the <TT
CLASS="LITERAL"
>emp</TT
> table:
</P><PRE
CLASS="SCREEN"
>CREATE FUNCTION clean_emp() RETURNS void AS '
DELETE FROM emp
WHERE salary < 0;
' LANGUAGE SQL;
SELECT clean_emp();
clean_emp
-----------
(1 row)</PRE
><P>
</P
><P
> The syntax of the <TT
CLASS="COMMAND"
>CREATE FUNCTION</TT
> command requires
the function body to be written as a string constant. It is usually
most convenient to use dollar quoting (see <A
HREF="sql-syntax-lexical.html#SQL-SYNTAX-DOLLAR-QUOTING"
>Section 4.1.2.2</A
>) for the string constant.
If you choose to use regular single-quoted string constant syntax,
you must double single quote marks (<TT
CLASS="LITERAL"
>'</TT
>) and backslashes
(<TT
CLASS="LITERAL"
>\</TT
>) (assuming escape string syntax) in the body of
the function (see <A
HREF="sql-syntax-lexical.html#SQL-SYNTAX-STRINGS"
>Section 4.1.2.1</A
>).
</P
><P
> Arguments to the SQL function are referenced in the function
body using the syntax <TT
CLASS="LITERAL"
>$<TT
CLASS="REPLACEABLE"
><I
>n</I
></TT
></TT
>: <TT
CLASS="LITERAL"
>$1</TT
>
refers to the first argument, <TT
CLASS="LITERAL"
>$2</TT
> to the second, and so on.
If an argument is of a composite type, then the dot notation,
e.g., <TT
CLASS="LITERAL"
>$1.name</TT
>, can be used to access attributes
of the argument. The arguments can only be used as data values,
not as identifiers. Thus for example this is reasonable:
</P><PRE
CLASS="PROGRAMLISTING"
>INSERT INTO mytable VALUES ($1);</PRE
><P>
but this will not work:
</P><PRE
CLASS="PROGRAMLISTING"
>INSERT INTO $1 VALUES (42);</PRE
><P>
</P
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="XFUNC-SQL-BASE-FUNCTIONS"
>34.4.1. <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> Functions on Base Types</A
></H2
><P
> The simplest possible <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> function has no arguments and
simply returns a base type, such as <TT
CLASS="TYPE"
>integer</TT
>:
</P><PRE
CLASS="SCREEN"
>CREATE FUNCTION one() RETURNS integer AS $$
SELECT 1 AS result;
$$ LANGUAGE SQL;
-- Alternative syntax for string literal:
CREATE FUNCTION one() RETURNS integer AS '
SELECT 1 AS result;
' LANGUAGE SQL;
SELECT one();
one
-----
1</PRE
><P>
</P
><P
> Notice that we defined a column alias within the function body for the result of the function
(with the name <TT
CLASS="LITERAL"
>result</TT
>), but this column alias is not visible
outside the function. Hence, the result is labeled <TT
CLASS="LITERAL"
>one</TT
>
instead of <TT
CLASS="LITERAL"
>result</TT
>.
</P
><P
> It is almost as easy to define <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> functions
that take base types as arguments. In the example below, notice
how we refer to the arguments within the function as <TT
CLASS="LITERAL"
>$1</TT
>
and <TT
CLASS="LITERAL"
>$2</TT
>.
</P><PRE
CLASS="SCREEN"
>CREATE FUNCTION add_em(integer, integer) RETURNS integer AS $$
SELECT $1 + $2;
$$ LANGUAGE SQL;
SELECT add_em(1, 2) AS answer;
answer
--------
3</PRE
><P>
</P
><P
> Here is a more useful function, which might be used to debit a
bank account:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE FUNCTION tf1 (integer, numeric) RETURNS integer AS $$
UPDATE bank
SET balance = balance - $2
WHERE accountno = $1;
SELECT 1;
$$ LANGUAGE SQL;</PRE
><P>
A user could execute this function to debit account 17 by $100.00 as
follows:
</P><PRE
CLASS="PROGRAMLISTING"
>SELECT tf1(17, 100.0);</PRE
><P>
</P
><P
> In practice one would probably like a more useful result from the
function than a constant 1, so a more likely definition
is:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE FUNCTION tf1 (integer, numeric) RETURNS numeric AS $$
UPDATE bank
SET balance = balance - $2
WHERE accountno = $1;
SELECT balance FROM bank WHERE accountno = $1;
$$ LANGUAGE SQL;</PRE
><P>
which adjusts the balance and returns the new balance.
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN40267"
>34.4.2. <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> Functions on Composite Types</A
></H2
><P
> When writing functions with arguments of composite
types, we must not only specify which
argument we want (as we did above with <TT
CLASS="LITERAL"
>$1</TT
> and <TT
CLASS="LITERAL"
>$2</TT
>) but
also the desired attribute (field) of that argument. For example,
suppose that
<TT
CLASS="TYPE"
>emp</TT
> is a table containing employee data, and therefore
also the name of the composite type of each row of the table. Here
is a function <CODE
CLASS="FUNCTION"
>double_salary</CODE
> that computes what someone's
salary would be if it were doubled:
</P><PRE
CLASS="SCREEN"
>CREATE TABLE emp (
name text,
salary numeric,
age integer,
cubicle point
);
CREATE FUNCTION double_salary(emp) RETURNS numeric AS $$
SELECT $1.salary * 2 AS salary;
$$ LANGUAGE SQL;
SELECT name, double_salary(emp.*) AS dream
FROM emp
WHERE emp.cubicle ~= point '(2,1)';
name | dream
------+-------
Bill | 8400</PRE
><P>
</P
><P
> Notice the use of the syntax <TT
CLASS="LITERAL"
>$1.salary</TT
>
to select one field of the argument row value. Also notice
how the calling <TT
CLASS="COMMAND"
>SELECT</TT
> command uses <TT
CLASS="LITERAL"
>*</TT
>
to select
the entire current row of a table as a composite value. The table
row can alternatively be referenced using just the table name,
like this:
</P><PRE
CLASS="SCREEN"
>SELECT name, double_salary(emp) AS dream
FROM emp
WHERE emp.cubicle ~= point '(2,1)';</PRE
><P>
but this usage is deprecated since it's easy to get confused.
</P
><P
> Sometimes it is handy to construct a composite argument value
on-the-fly. This can be done with the <TT
CLASS="LITERAL"
>ROW</TT
> construct.
For example, we could adjust the data being passed to the function:
</P><PRE
CLASS="SCREEN"
>SELECT name, double_salary(ROW(name, salary*1.1, age, cubicle)) AS dream
FROM emp;</PRE
><P>
</P
><P
> It is also possible to build a function that returns a composite type.
This is an example of a function
that returns a single <TT
CLASS="TYPE"
>emp</TT
> row:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE FUNCTION new_emp() RETURNS emp AS $$
SELECT text 'None' AS name,
1000.0 AS salary,
25 AS age,
point '(2,2)' AS cubicle;
$$ LANGUAGE SQL;</PRE
><P>
In this example we have specified each of the attributes
with a constant value, but any computation
could have been substituted for these constants.
</P
><P
> Note two important things about defining the function:
<P
></P
></P><UL
><LI
><P
> The select list order in the query must be exactly the same as
that in which the columns appear in the table associated
with the composite type. (Naming the columns, as we did above,
is irrelevant to the system.)
</P
></LI
><LI
><P
> You must typecast the expressions to match the
definition of the composite type, or you will get errors like this:
</P><PRE
CLASS="SCREEN"
><SAMP
CLASS="COMPUTEROUTPUT"
>ERROR: function declared to return emp returns varchar instead of text at column 1</SAMP
></PRE
><P>
</P
></LI
></UL
><P>
</P
><P
> A different way to define the same function is:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE FUNCTION new_emp() RETURNS emp AS $$
SELECT ROW('None', 1000.0, 25, '(2,2)')::emp;
$$ LANGUAGE SQL;</PRE
><P>
Here we wrote a <TT
CLASS="COMMAND"
>SELECT</TT
> that returns just a single
column of the correct composite type. This isn't really better
in this situation, but it is a handy alternative in some cases
— for example, if we need to compute the result by calling
another function that returns the desired composite value.
</P
><P
> We could call this function directly in either of two ways:
</P><PRE
CLASS="SCREEN"
>SELECT new_emp();
new_emp
--------------------------
(None,1000.0,25,"(2,2)")
SELECT * FROM new_emp();
name | salary | age | cubicle
------+--------+-----+---------
None | 1000.0 | 25 | (2,2)</PRE
><P>
The second way is described more fully in <A
HREF="xfunc-sql.html#XFUNC-SQL-TABLE-FUNCTIONS"
>Section 34.4.4</A
>.
</P
><P
> When you use a function that returns a composite type,
you might want only one field (attribute) from its result.
You can do that with syntax like this:
</P><PRE
CLASS="SCREEN"
>SELECT (new_emp()).name;
name
------
None</PRE
><P>
The extra parentheses are needed to keep the parser from getting
confused. If you try to do it without them, you get something like this:
</P><PRE
CLASS="SCREEN"
>SELECT new_emp().name;
ERROR: syntax error at or near "." at character 17
LINE 1: SELECT new_emp().name;
^</PRE
><P>
</P
><P
> Another option is to use
functional notation for extracting an attribute. The simple way
to explain this is that we can use the
notations <TT
CLASS="LITERAL"
>attribute(table)</TT
> and <TT
CLASS="LITERAL"
>table.attribute</TT
>
interchangeably.
</P><PRE
CLASS="SCREEN"
>SELECT name(new_emp());
name
------
None</PRE
><P>
</P><PRE
CLASS="SCREEN"
>-- This is the same as:
-- SELECT emp.name AS youngster FROM emp WHERE emp.age < 30;
SELECT name(emp) AS youngster FROM emp WHERE age(emp) < 30;
youngster
-----------
Sam
Andy</PRE
><P>
</P
><DIV
CLASS="TIP"
><BLOCKQUOTE
CLASS="TIP"
><P
><B
>Tip: </B
> The equivalence between functional notation and attribute notation
makes it possible to use functions on composite types to emulate
<SPAN
CLASS="QUOTE"
>"computed fields"</SPAN
>.
<A
NAME="AEN40312"
></A
>
<A
NAME="AEN40314"
></A
>
For example, using the previous definition
for <TT
CLASS="LITERAL"
>double_salary(emp)</TT
>, we can write
</P><PRE
CLASS="SCREEN"
>SELECT emp.name, emp.double_salary FROM emp;</PRE
><P>
An application using this wouldn't need to be directly aware that
<TT
CLASS="LITERAL"
>double_salary</TT
> isn't a real column of the table.
(You can also emulate computed fields with views.)
</P
></BLOCKQUOTE
></DIV
><P
> Another way to use a function returning a composite type is to pass the
result to another function that accepts the correct row type as input:
</P><PRE
CLASS="SCREEN"
>CREATE FUNCTION getname(emp) RETURNS text AS $$
SELECT $1.name;
$$ LANGUAGE SQL;
SELECT getname(new_emp());
getname
---------
None
(1 row)</PRE
><P>
</P
><P
> Still another way to use a function that returns a composite type is to
call it as a table function, as described in <A
HREF="xfunc-sql.html#XFUNC-SQL-TABLE-FUNCTIONS"
>Section 34.4.4</A
>.
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="XFUNC-OUTPUT-PARAMETERS"
>34.4.3. Functions with Output Parameters</A
></H2
><A
NAME="AEN40326"
></A
><P
> An alternative way of describing a function's results is to define it
with <I
CLASS="FIRSTTERM"
>output parameters</I
>, as in this example:
</P><PRE
CLASS="SCREEN"
>CREATE FUNCTION add_em (IN x int, IN y int, OUT sum int)
AS 'SELECT $1 + $2'
LANGUAGE SQL;
SELECT add_em(3,7);
add_em
--------
10
(1 row)</PRE
><P>
This is not essentially different from the version of <TT
CLASS="LITERAL"
>add_em</TT
>
shown in <A
HREF="xfunc-sql.html#XFUNC-SQL-BASE-FUNCTIONS"
>Section 34.4.1</A
>. The real value of
output parameters is that they provide a convenient way of defining
functions that return several columns. For example,
</P><PRE
CLASS="SCREEN"
>CREATE FUNCTION sum_n_product (x int, y int, OUT sum int, OUT product int)
AS 'SELECT $1 + $2, $1 * $2'
LANGUAGE SQL;
SELECT * FROM sum_n_product(11,42);
sum | product
-----+---------
53 | 462
(1 row)</PRE
><P>
What has essentially happened here is that we have created an anonymous
composite type for the result of the function. The above example has
the same end result as
</P><PRE
CLASS="SCREEN"
>CREATE TYPE sum_prod AS (sum int, product int);
CREATE FUNCTION sum_n_product (int, int) RETURNS sum_prod
AS 'SELECT $1 + $2, $1 * $2'
LANGUAGE SQL;</PRE
><P>
but not having to bother with the separate composite type definition
is often handy.
</P
><P
> Notice that output parameters are not included in the calling argument
list when invoking such a function from SQL. This is because
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> considers only the input
parameters to define the function's calling signature. That means
also that only the input parameters matter when referencing the function
for purposes such as dropping it. We could drop the above function
with either of
</P><PRE
CLASS="SCREEN"
>DROP FUNCTION sum_n_product (x int, y int, OUT sum int, OUT product int);
DROP FUNCTION sum_n_product (int, int);</PRE
><P>
</P
><P
> Parameters can be marked as <TT
CLASS="LITERAL"
>IN</TT
> (the default),
<TT
CLASS="LITERAL"
>OUT</TT
>, or <TT
CLASS="LITERAL"
>INOUT</TT
>. An <TT
CLASS="LITERAL"
>INOUT</TT
>
parameter serves as both an input parameter (part of the calling
argument list) and an output parameter (part of the result record type).
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="XFUNC-SQL-TABLE-FUNCTIONS"
>34.4.4. <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> Functions as Table Sources</A
></H2
><P
> All SQL functions can be used in the <TT
CLASS="LITERAL"
>FROM</TT
> clause of a query,
but it is particularly useful for functions returning composite types.
If the function is defined to return a base type, the table function
produces a one-column table. If the function is defined to return
a composite type, the table function produces a column for each attribute
of the composite type.
</P
><P
> Here is an example:
</P><PRE
CLASS="SCREEN"
>CREATE TABLE foo (fooid int, foosubid int, fooname text);
INSERT INTO foo VALUES (1, 1, 'Joe');
INSERT INTO foo VALUES (1, 2, 'Ed');
INSERT INTO foo VALUES (2, 1, 'Mary');
CREATE FUNCTION getfoo(int) RETURNS foo AS $$
SELECT * FROM foo WHERE fooid = $1;
$$ LANGUAGE SQL;
SELECT *, upper(fooname) FROM getfoo(1) AS t1;
fooid | foosubid | fooname | upper
-------+----------+---------+-------
1 | 1 | Joe | JOE
(1 row)</PRE
><P>
As the example shows, we can work with the columns of the function's
result just the same as if they were columns of a regular table.
</P
><P
> Note that we only got one row out of the function. This is because
we did not use <TT
CLASS="LITERAL"
>SETOF</TT
>. That is described in the next section.
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN40353"
>34.4.5. <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> Functions Returning Sets</A
></H2
><P
> When an SQL function is declared as returning <TT
CLASS="LITERAL"
>SETOF
<TT
CLASS="REPLACEABLE"
><I
>sometype</I
></TT
></TT
>, the function's final
<TT
CLASS="COMMAND"
>SELECT</TT
> query is executed to completion, and each row it
outputs is returned as an element of the result set.
</P
><P
> This feature is normally used when calling the function in the <TT
CLASS="LITERAL"
>FROM</TT
>
clause. In this case each row returned by the function becomes
a row of the table seen by the query. For example, assume that
table <TT
CLASS="LITERAL"
>foo</TT
> has the same contents as above, and we say:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE FUNCTION getfoo(int) RETURNS SETOF foo AS $$
SELECT * FROM foo WHERE fooid = $1;
$$ LANGUAGE SQL;
SELECT * FROM getfoo(1) AS t1;</PRE
><P>
Then we would get:
</P><PRE
CLASS="SCREEN"
> fooid | foosubid | fooname
-------+----------+---------
1 | 1 | Joe
1 | 2 | Ed
(2 rows)</PRE
><P>
</P
><P
> It is also possible to return multiple rows with the columns defined by
output parameters, like this:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE FUNCTION sum_n_product_with_tab (x int, OUT sum int, OUT product int) RETURNS SETOF record AS $$
SELECT x + tab.y, x * tab.y FROM tab;
$$ LANGUAGE SQL;</PRE
><P>
The key point here is that you must write <TT
CLASS="LITERAL"
>RETURNS SETOF record</TT
>
to indicate that the function returns multiple rows instead of just one.
If there is only one output parameter, write that parameter's type
instead of <TT
CLASS="TYPE"
>record</TT
>.
</P
><P
> Currently, functions returning sets can also be called in the select list
of a query. For each row that the query
generates by itself, the function returning set is invoked, and an output
row is generated for each element of the function's result set. Note,
however, that this capability is deprecated and might be removed in future
releases. The following is an example function returning a set from the
select list:
</P><PRE
CLASS="SCREEN"
>CREATE FUNCTION listchildren(text) RETURNS SETOF text AS $$
SELECT name FROM nodes WHERE parent = $1
$$ LANGUAGE SQL;
SELECT * FROM nodes;
name | parent
-----------+--------
Top |
Child1 | Top
Child2 | Top
Child3 | Top
SubChild1 | Child1
SubChild2 | Child1
(6 rows)
SELECT listchildren('Top');
listchildren
--------------
Child1
Child2
Child3
(3 rows)
SELECT name, listchildren(name) FROM nodes;
name | listchildren
--------+--------------
Top | Child1
Top | Child2
Top | Child3
Child1 | SubChild1
Child1 | SubChild2
(5 rows)</PRE
><P>
In the last <TT
CLASS="COMMAND"
>SELECT</TT
>,
notice that no output row appears for <TT
CLASS="LITERAL"
>Child2</TT
>, <TT
CLASS="LITERAL"
>Child3</TT
>, etc.
This happens because <CODE
CLASS="FUNCTION"
>listchildren</CODE
> returns an empty set
for those arguments, so no result rows are generated.
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN40375"
>34.4.6. Polymorphic <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> Functions</A
></H2
><P
> <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> functions can be declared to accept and
return the polymorphic types <TT
CLASS="TYPE"
>anyelement</TT
>,
<TT
CLASS="TYPE"
>anyarray</TT
>, <TT
CLASS="TYPE"
>anynonarray</TT
>, and
<TT
CLASS="TYPE"
>anyenum</TT
>. See <A
HREF="extend-type-system.html#EXTEND-TYPES-POLYMORPHIC"
>Section 34.2.5</A
> for a more detailed
explanation of polymorphic functions. Here is a polymorphic
function <CODE
CLASS="FUNCTION"
>make_array</CODE
> that builds up an array
from two arbitrary data type elements:
</P><PRE
CLASS="SCREEN"
>CREATE FUNCTION make_array(anyelement, anyelement) RETURNS anyarray AS $$
SELECT ARRAY[$1, $2];
$$ LANGUAGE SQL;
SELECT make_array(1, 2) AS intarray, make_array('a'::text, 'b') AS textarray;
intarray | textarray
----------+-----------
{1,2} | {a,b}
(1 row)</PRE
><P>
</P
><P
> Notice the use of the typecast <TT
CLASS="LITERAL"
>'a'::text</TT
>
to specify that the argument is of type <TT
CLASS="TYPE"
>text</TT
>. This is
required if the argument is just a string literal, since otherwise
it would be treated as type
<TT
CLASS="TYPE"
>unknown</TT
>, and array of <TT
CLASS="TYPE"
>unknown</TT
> is not a valid
type.
Without the typecast, you will get errors like this:
</P><PRE
CLASS="SCREEN"
><SAMP
CLASS="COMPUTEROUTPUT"
>ERROR: could not determine polymorphic type because input has type "unknown"</SAMP
></PRE
><P>
</P
><P
> It is permitted to have polymorphic arguments with a fixed
return type, but the converse is not. For example:
</P><PRE
CLASS="SCREEN"
>CREATE FUNCTION is_greater(anyelement, anyelement) RETURNS boolean AS $$
SELECT $1 > $2;
$$ LANGUAGE SQL;
SELECT is_greater(1, 2);
is_greater
------------
f
(1 row)
CREATE FUNCTION invalid_func() RETURNS anyelement AS $$
SELECT 1;
$$ LANGUAGE SQL;
ERROR: cannot determine result data type
DETAIL: A function returning a polymorphic type must have at least one polymorphic argument.</PRE
><P>
</P
><P
> Polymorphism can be used with functions that have output arguments.
For example:
</P><PRE
CLASS="SCREEN"
>CREATE FUNCTION dup (f1 anyelement, OUT f2 anyelement, OUT f3 anyarray)
AS 'select $1, array[$1,$1]' LANGUAGE sql;
SELECT * FROM dup(22);
f2 | f3
----+---------
22 | {22,22}
(1 row)</PRE
><P>
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