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Improve documentation for COALESCE and NULLIF. Add references for NVL

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and IFNULL.

Backpatch to 8.1.X.
This commit is contained in:
Bruce Momjian 2005-11-28 23:18:48 +00:00
parent 200545039c
commit ee4aa3021e
1 changed files with 23 additions and 11 deletions
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34
doc/src/sgml/func.sgml
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@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.295 2005/11/19 19:44:54 tgl Exp $
$PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.296 2005/11/28 23:18:48 momjian Exp $
PostgreSQL documentation
-->
@ -7227,6 +7227,14 @@ SELECT ... WHERE CASE WHEN x &lt;&gt; 0 THEN y/x &gt; 1.5 ELSE false END;
<primary>COALESCE</primary>
</indexterm>
<indexterm>
<primary>NVL</primary>
</indexterm>
<indexterm>
<primary>IFNULL</primary>
</indexterm>
<synopsis>
<function>COALESCE</function>(<replaceable>value</replaceable> <optional>, ...</optional>)
</synopsis>
@ -7234,9 +7242,8 @@ SELECT ... WHERE CASE WHEN x &lt;&gt; 0 THEN y/x &gt; 1.5 ELSE false END;
<para>
The <function>COALESCE</function> function returns the first of its
arguments that is not null. Null is returned only if all arguments
are null. This is often useful to substitute a
default value for null values when data is retrieved for display,
for example:
are null. It is often used to substitute a default value for
null values when data is retrieved for display, for example:
<programlisting>
SELECT COALESCE(description, short_description, '(none)') ...
</programlisting>
@ -7246,7 +7253,9 @@ SELECT COALESCE(description, short_description, '(none)') ...
Like a <token>CASE</token> expression, <function>COALESCE</function> will
not evaluate arguments that are not needed to determine the result;
that is, arguments to the right of the first non-null argument are
not evaluated.
not evaluated. This SQL-standard function provides capabilities similar
to <function>NVL</> and <function>IFNULL</>, which are used in some other
database systems.
</para>
</sect2>
@ -7262,16 +7271,19 @@ SELECT COALESCE(description, short_description, '(none)') ...
</synopsis>
<para>
The <function>NULLIF</function> function returns a null value if and only
if <replaceable>value1</replaceable> and
<replaceable>value2</replaceable> are equal. Otherwise it returns
<replaceable>value1</replaceable>. This can be used to perform the
inverse operation of the <function>COALESCE</function> example
given above:
The <function>NULLIF</function> function returns a null value if
<replaceable>value1</replaceable> and <replaceable>value2</replaceable>
are equal; otherwise it returns <replaceable>value1</replaceable>.
This can be used to perform the inverse operation of the
<function>COALESCE</function> example given above:
<programlisting>
SELECT NULLIF(value, '(none)') ...
</programlisting>
</para>
<para>
If <replaceable>value1</replaceable> is <literal>(none)</>, return a null,
otherwise return <replaceable>value1</replaceable>.
</para>
</sect2>