Help with creating a user function

Question

Hi, I have never created a user function in Oracle and need some help. My function takes in a variable, reads the table looking for a match of the first 2 characters, if not found tries based on the first character. This is what I have so far:
CREATE function Get_Country_Of_Origin
(av_SERIAL_ID varchar2)
RETURN varchar2
IS
var_country varchar2;
BEGIN
--If match on first 2 characters of serial id return that value
SELECT DESCRIPTION INTO var_country
FROM M4LOADER.SUPPLIER_TYPE
WHERE SUPPLIER_TYPE = LEFT(av_SERIAL_ID,2)
--Else If match on first character of serial id return that value
SELECT DESCRIPTION INTO var_country
FROM M4LOADER.SUPPLIER_TYPE
WHERE SUPPLIER_TYPE = LEFT(av_SERIAL_ID,1)
--Else return nothing
return var_country;
END;

Answer 1

<FONT FACE="Arial" size=2 color="2D0000">
CREATE function Get_Country_Of_Origin (av_SERIAL_ID varchar2)
RETURN varchar2
IS
var_country varchar2;
BEGIN
--If match on first 2 characters of serial id return that value
<font color="#ff8040">Are you sure that the following will return only one single value </font><font color="#800000">( if TO MANY ROWS ARE FOUND then ..?)</font>
SELECT DESCRIPTION INTO var_country FROM M4LOADER.SUPPLIER_TYPE WHERE SUPPLIER_TYPE = <font color="#0080c0">substr(av_SERIAL_ID,0,2)</font>
--Else If match on first character of serial id return that value
<font color="#0d1099">IF var_country is null then</font>
SELECT DESCRIPTION INTO var_country FROM M4LOADER.SUPPLIER_TYPE WHERE SUPPLIER_TYPE = <font color="#0080c0">substr(av_SERIAL_ID,0,1)</font>
<font color="#0d1099">End if;</font></font>
return var_country;
END;
-SK
</FONT>