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Document IS DISTINCT FROM in a more obvious place, and add some more 

index entries for IS-foo constructs.
This commit is contained in:
Tom Lane 2004-10-26 22:16:12 +00:00
parent 3b6cc1ad6d
commit 3d2849820b
2 changed files with 86 additions and 9 deletions
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81
doc/src/sgml/func.sgml
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@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.220 2004/10/04 08:15:41 neilc Exp $
$PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.221 2004/10/26 22:16:11 tgl Exp $
PostgreSQL documentation
-->
@ -283,6 +283,18 @@ PostgreSQL documentation
</para>
<para>
<indexterm>
<primary>IS NULL</primary>
</indexterm>
<indexterm>
<primary>IS NOT NULL</primary>
</indexterm>
<indexterm>
<primary>ISNULL</primary>
</indexterm>
<indexterm>
<primary>NOTNULL</primary>
</indexterm>
To check whether a value is or is not null, use the constructs
<synopsis>
<replaceable>expression</replaceable> IS NULL
@ -305,6 +317,7 @@ PostgreSQL documentation
behavior conforms to the SQL standard.
</para>
<tip>
<para>
Some applications may expect that
<literal><replaceable>expression</replaceable> = NULL</literal>
@ -318,8 +331,43 @@ PostgreSQL documentation
the default behavior in <productname>PostgreSQL</productname>
releases 6.5 through 7.1.
</para>
</tip>
<para>
<indexterm>
<primary>IS DISTINCT FROM</primary>
</indexterm>
The ordinary comparison operators yield null (signifying <quote>unknown</>)
when either input is null. Another way to do comparisons is with the
<literal>IS DISTINCT FROM</literal> construct:
<synopsis>
<replaceable>expression</replaceable> IS DISTINCT FROM <replaceable>expression</replaceable>
</synopsis>
For non-null inputs this is the same as the <literal>&lt;&gt;</> operator.
However, when both inputs are null it will return false, and when just
one input is null it will return true. Thus it effectively acts as though
null were a normal data value, rather than <quote>unknown</>.
</para>
<para>
<indexterm>
<primary>IS TRUE</primary>
</indexterm>
<indexterm>
<primary>IS NOT TRUE</primary>
</indexterm>
<indexterm>
<primary>IS FALSE</primary>
</indexterm>
<indexterm>
<primary>IS NOT FALSE</primary>
</indexterm>
<indexterm>
<primary>IS UNKNOWN</primary>
</indexterm>
<indexterm>
<primary>IS NOT UNKNOWN</primary>
</indexterm>
Boolean values can also be tested using the constructs
<synopsis>
<replaceable>expression</replaceable> IS TRUE
@ -329,9 +377,13 @@ PostgreSQL documentation
<replaceable>expression</replaceable> IS UNKNOWN
<replaceable>expression</replaceable> IS NOT UNKNOWN
</synopsis>
These are similar to <literal>IS NULL</literal> in that they will
always return true or false, never a null value, even when the operand is null.
These will always return true or false, never a null value, even when the
operand is null.
A null input is treated as the logical value <quote>unknown</>.
Notice that <literal>IS UNKNOWN</> and <literal>IS NOT UNKNOWN</> are
effectively the same as <literal>IS NULL</literal> and
<literal>IS NOT NULL</literal>, respectively, except that the input
expression must be of Boolean type.
</para>
</sect1>
@ -7344,7 +7396,7 @@ SELECT col1 FROM tab1
</sect2>
<sect2>
<title><literal>NOT IN </literal></title>
<title><literal>NOT IN</literal></title>
<synopsis>
<replaceable>expression</replaceable> NOT IN (<replaceable>subquery</replaceable>)
@ -7538,9 +7590,9 @@ SELECT col1 FROM tab1
<sect2>
<title>Row-wise Comparison</title>
<indexterm>
<indexterm zone="functions-subquery">
<primary>comparison</primary>
<secondary>of rows</secondary>
<secondary>subquery result row</secondary>
</indexterm>
<synopsis>
@ -7594,6 +7646,23 @@ SELECT col1 FROM tab1
<primary>SOME</primary>
</indexterm>
<indexterm>
<primary>comparison</primary>
<secondary>row-wise</secondary>
</indexterm>
<indexterm>
<primary>IS DISTINCT FROM</primary>
</indexterm>
<indexterm>
<primary>IS NULL</primary>
</indexterm>
<indexterm>
<primary>IS NOT NULL</primary>
</indexterm>
<para>
This section describes several specialized constructs for making
multiple comparisons between groups of values. These forms are

14
doc/src/sgml/syntax.sgml
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@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/syntax.sgml,v 1.95 2004/09/20 22:48:25 tgl Exp $
$PostgreSQL: pgsql/doc/src/sgml/syntax.sgml,v 1.96 2004/10/26 22:16:12 tgl Exp $
-->
<chapter id="sql-syntax">
@ -1421,6 +1421,10 @@ SELECT name, (SELECT max(pop) FROM cities WHERE cities.state = states.name)
<secondary>constructor</secondary>
</indexterm>
<indexterm>
<primary>ARRAY</primary>
</indexterm>
<para>
An array constructor is an expression that builds an
array value from values for its member elements. A simple array
@ -1521,13 +1525,17 @@ SELECT ARRAY(SELECT oid FROM pg_proc WHERE proname LIKE 'bytea%');
<secondary>constructor</secondary>
</indexterm>
<indexterm>
<primary>ROW</primary>
</indexterm>
<para>
A row constructor is an expression that builds a row value (also
called a composite value) from values
for its member fields. A row constructor consists of the key word
<literal>ROW</literal>, a left parenthesis <literal>(</>, zero or more
<literal>ROW</literal>, a left parenthesis, zero or more
expressions (separated by commas) for the row field values, and finally
a right parenthesis <literal>)</>. For example,
a right parenthesis. For example,
<programlisting>
SELECT ROW(1,2.5,'this is a test');
</programlisting>