diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml index b6f1a40b4a0a46c293b852be5a352d1e1d43a943..7d603ef97822848a61f278ca0331aabfe6e0e3cd 100644 --- a/doc/src/sgml/func.sgml +++ b/doc/src/sgml/func.sgml @@ -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 <> 0 THEN y/x > 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 <> 0 THEN y/x > 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>