pl/pgsql question (functions)

Greetings,

I am new to pl/pgsqm (I did some SQL programming at school, now 8 years
ago so that part is rusty too ;-))

Anycase, I have a question concerning creating your own functions in
pl/pgsql.

This is my situation:

I have two tables:
- 'hosts': containing 'hostname' (primary key) and 'ip_address' (unique
and non null).
- 'aliases': containing 'aliasname' (primary key) and 'hostname'(unique
and non null).
- aliasname.hostname is a foreign reference to hosts.hostname

Further, I've set up a trigger function in both hosts and aliases; so that
a name cannot be in both tables.

So far, so good.

Now, I would like to create a function 'get_ip_address' that ... euh ...
retrieves an IP-address (one argument: hostname).
- If the hostname is in the table 'hosts', return the corresponding
IP-address.
- If the hostname is in the table 'aliases', return the IP-address of the
corresponding hostname in 'hosts'.
- If the hostname is in neither table, return nothing.

(See program below):

The 'problem' is in the case where the data in in neither field. How do I
program this?

- If there is no 'RETURN' statement for that case; I get an error
'function terminated without RETURN'.
- Just <RETURN>, <RETURN ""> or <RETURN ''> all produce an syntax-error.
- When I do '<RETURN ret>' (ret being the result of the last query, being
the query in the 'aliases' table; I do NOT get an error; but the function
does return something (an empty row).

This I don't like for two reasons:
1/ When you do 'select ... from ... where ...', and the query doesn't
'find' anything; you get NOTHING (no rows).

When I do get_ip_addr('something_that_does_not_exist'); I do get
SOMETHING: one row (containing an empty field).

2/ When another function uses the "get_ip_addr('some_host')" function; I
cannot use 'IF NOT FOUND ...'; as -even when 'some_host' does not exist,
the function returns something. (hence, the 'IF NOT FOUND' case is never
followed).

So, does anybody any idea how to 'fix' this?

For some reason, I get the feeling I have the wrong 'concept' of functions
in pl/pgsql.
I am using functions in the wrong 'way'?

Here's the program:

--- cut here --- begin --- cut here ---
DECLARE
ret inet;

BEGIN
select into ret
ipaddr from hosts
where hostname = $1;

IF FOUND
THEN
RETURN ret;
ELSE
select into ret
ipaddr from hosts,aliases
where
hosts.hostname = aliases.hostname
AND aliases.aliasname = $1;

IF FOUND
THEN
RETURN ret;
ELSE
-- Problem, what should I put here ???
RETURN;
END IF;
END IF;

END;
--- cut here --- end --- cut here ---

Cheerio! Kr. Bonne.
--
KB905-RIPE Belgacom IP networking
(c=be,a=rtt,p=belgacomgroup,s=Bonne,g=Kristoff) Internet, IP and IP/VPN
kristoff(dot)bonne(at)skypro(dot)be Faxbox : +32 2 2435122