-<!-- $PostgreSQL: pgsql/doc/src/sgml/ddl.sgml,v 1.92 2010/04/03 07:22:53 petere Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/ddl.sgml,v 1.93 2010/04/06 02:18:04 momjian Exp $ -->
<chapter id="ddl">
<title>Data Definition</title>
<para>
Exclusion constraints ensure that if any two rows are compared on
the specified columns or expressions using the specified operators,
- at least one of these operator comparisons will be false. The syntax is:
+ at least one of these operator comparisons will return false or null.
+ The syntax is:
<programlisting>
CREATE TABLE circles (
c circle,