<literal>IS NULL</literal> and <literal>IS NOT NULL</literal> do not always return

inverse results for row-valued expressions; in particular, a row-valued

expression that contains both null and non-null fields will return false

for both tests. In some cases, it may be preferable to

for both tests. For example:

<programlisting>

SELECT ROW(1,2.5,'this is a test') = ROW(1, 3, 'not the same');

SELECT ROW(table.*) IS NULL FROM table; -- detect all-null rows

SELECT ROW(table.*) IS NOT NULL FROM table; -- detect all-non-null rows

SELECT NOT(ROW(table.*) IS NOT NULL) FROM TABLE; -- detect at least one null in rows

</programlisting>

In some cases, it may be preferable to

write <replaceable>row</replaceable> <literal>IS DISTINCT FROM NULL</literal>

or <replaceable>row</replaceable> <literal>IS NOT DISTINCT FROM NULL</literal>,

which will simply check whether the overall row value is null without any

<para>

Row constructors can be used to build composite values to be stored

in a composite-type table column, or to be passed to a function that

accepts a composite parameter. Also,

it is possible to compare two row values or test a row with

<literal>IS NULL</literal> or <literal>IS NOT NULL</literal>, for example:

<programlisting>

SELECT ROW(1,2.5,'this is a test') = ROW(1, 3, 'not the same');

SELECT ROW(table.*) IS NULL FROM table; -- detect all-null rows

</programlisting>

For more detail see <xref linkend="functions-comparisons"/>.

Row constructors can also be used in connection with subqueries,

as discussed in <xref linkend="functions-subquery"/>.

accepts a composite parameter. Also, it is possible to test rows

using the standard comparison operators as described in <xref

linkend="functions-comparison"/>, to compare one row against another

as described in <xref linkend="functions-comparisons"/>, and to

use them in connection with subqueries, as discussed in <xref

linkend="functions-subquery"/>,

</para>

</sect2>