$PostgreSQL: pgsql/doc/src/sgml/typeconv.sgml,v 1.39 2003/11/29 19:51:38 pgsql Exp $

<para>

On the other hand, the postfix operator <literal>!</> (factorial)

is defined only for integer data types, not for <type>float8</type>. So, if we

try a similar case with <literal>!</>, we get:

<screen>

SELECT '20' ! AS "factorial";

ERROR: operator is not unique: "unknown" !

HINT: Could not choose a best candidate operator. You may need to add explicit

type casts.

</screen>

This happens because the system can't decide which of the several

possible <literal>!</> operators should be preferred. We can help

it out with an explicit cast:

<screen>

SELECT CAST('20' AS int8) ! AS "factorial";

factorial

---------------------

2432902008176640000

(1 row)

</screen>

</para>