IFNULL - problem

Hi, I'm using PostgreSQL 6.5.1, and when I try to use IFNULL (listed
in the SQL Functions section of the docs in
/doc.html/user/functions.htm#AEN2121, as:
  Table 5-1. SQL Functions  Function Returns Description Example  ...  IFNULL(input,non-NULL substitute) non-NULL
returnsecond argument if  first is NULL IFNULL(c1, 'N/A')  ...
 

), psql complains about not knowing such a function:

albert=> select ifnull(NULL, 'ASDF');
ERROR:  No such function 'ifnull' with the specified attributes
albert=> select ifnull(1, 2);
ERROR:  No such function 'ifnull' with the specified attributes

What I really want to do is something like:

albert=> \d mailcalendar
Table    = mailcalendar
+----------------------------------+----------------------------------+-------+
|              Field               |              Type                | Length|
+----------------------------------+----------------------------------+-------+
| base                             | datetime                         |     8 |
| repeat                           | reltime                          |     4 |
| offs                             | reltime                          |     4 |
| next                             | datetime                         |     8 |
| mail                             | text                             |   var |
+----------------------------------+----------------------------------+-------+
albert=> select ifnull(next, base) as asdf from mailcalendar;
ERROR:  No such function 'ifnull' with the specified attributes

What's wrong here? Am I just misusing this feature, or is it really
missing? I know that I can work around it by using case, but this is a
bit less convenient.

albert=> select case when next is null then base else next end as asdf from mailcalendar;
asdf
----------------------------
Sun Sep 26 00:00:00 1971 MET
(1 row)


Albert.

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