Parmeter testing condition

Question

I am converting some ingress procedures into PL/SQL and have a situation where
based on the results (i.e. rows returned) I execute different code.
So I have a v_file_name_found parameter that is defined locally to the procedure.
The procedure is passed in a file name and I search for it ...
If found I then assign it to the v_file_name_found , if
the where clause was met. If I get 0 rows back, I do A, if I get rows > 0 then I do B.
In oracle do I have to assign the v_file_name since all I am doing is testing out the
conditions of the where clause ?
Here's the Ingress code with a smattering of oraclese that I am adding for the conversion ..
create or replace procedure   msg_read  (file_name in char)
user authid
v_file_name_found    char;
Begin
select a.file_name into v_file_name_found
  from table One A, Table Two B
where a.file_name = b.file_name and
a.vol_id = vol_id;
if sqlcode <> 0  then  ... do something  AAA
else
if iirowcound = 0  then   do BBB
end;
/Thank you for your insight.
Edited by: BluShadow on 16-May-2011 15:11
added {noformat}{noformat} tags and fixed the <> symbols that don't appear together on the forum.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   

Answer 1

Hi,
What you have is a good way to do it in Oracle.
You have to SELECT INTO something, so you need a variable. If all you really want to know is whether the query found something or not, then you can do something like this:
CREATE OR REPLACE PROCEDURE msg_read (in_file_name IN VARCHAR2)
AUTHID CURRENT_USER
IS
     v_file_name_found     a.file_name%TYPE;
BEGIN
    BEGIN
            SELECT     a.file_name
     INTO     v_file_name_found
     FROM     table_One A
     ,     Table_Two B
     WHERE     a.file_name     = b.file_name
     AND     a.vol_id          = vol_id
     AND     ROWNUM          = 1;
     -- Do AAA
    EXCEPTION
        WHEN  NO_DATA_FOUND
     THEN
         -- Do BBB
    END;    -- End of nested BEGIN block
    -- The following code is done in all cases (unless a real error occurred) after AAA or BBB
END     msg_read;where you catch the error that occurs when the query returns 0 rows. However, you still need to SELECT INTO a variable, so in this case, I don't think thie approach above gains anything for you. Keep on doing it the way you thought of.
I haven't tested the code above, but I know it's closer to the correct Oracle syntax.
Don't use the CHAR datatype. Use VARCHAR2 or, if you want to specify that a local variable is the same type and size as some database column, use %TYPE, as I did above.
If file_name is the name of a column, then you should choose another name for the parameter, such as file_name_given or in_file_name. It's not necessarily an error to use the same name, but it can cause confusion.
If a SELECT INTO statement finds more that 1 row, it will raise the TOO_MANY_ROWS error. You could test for that in the EXCEPTION section of a nested block, but it's easier to avoid it altogether by
(a) using ROWNUM = 1, as shown above
(b) re-writing the query to use aggregate functions (but no GROUP BY), or
(c) re-writng the query as an EXISTS sub-query, as in "SELECT 1 FROM dual WHERE EXISTS (...)"
Edited by: Frank Kulash on May 16, 2011 10:18 AM