In some cases it is useful to define table functions that can

return different column sets depending on how they are invoked.

To support this, the table function can be declared as returning

the pseudo-type <type>record</>. When such a function is used in

the pseudo-type <type>record</> with no <literal>OUT</literal>

parameters. When such a function is used in

a query, the expected row structure must be specified in the

query itself, so that the system can know how to parse and plan

the query. This syntax looks like:

that the parser knows, for example, what <literal>*</> should

expand to.

</para>

<para>

This example uses <literal>ROWS FROM</literal>:

<programlisting>

SELECT *

FROM ROWS FROM

(

json_to_recordset('[{"a":40,"b":"foo"},{"a":"100","b":"bar"}]')

AS (a INTEGER, b TEXT),

generate_series(1, 3)

) AS x (p, q, s)

ORDER BY p;

p | q | s

-----+-----+---

40 | foo | 1

100 | bar | 2

| | 3

</programlisting>

It joins two functions into a single <literal>FROM</literal>

target. <function>json_to_recordset()</function> is instructed

to return two columns, the first <type>integer</type>

and the second <type>text</type>. The result of

<function>generate_series()</function> is used directly.

The <literal>ORDER BY</literal> clause sorts the column values

as integers.

</para>

</sect3>

<sect3 id="queries-lateral">