How to test for différent Select into a single PL/SQL block ?

Question

Hi,
I am relatively new to PL/SQL and I am trying to do multiple selects int a single PL/SQL block. I am confronted to the fact that if a single select returns no data, I have to go to the WHEN DATA_NOT_FOUND exception.
Or, I would like to test for different selects.
In an authentification script, I am searching in a table for a USER ID (USERID) and an application ID, to check if a user is registered under this USERID for this APPLICATION.
There are different possibilities : 4 possibilities :
- USERID Existing or not Existing and
- Aplication ID found or not found for this particular USERID.
I would like to test for thes 4 possibilities to get the status of this partiular user regardin this application.
The problem is that if one select returns no row, I go to the exception data not found.
In the example below you see that if no row returned, go to the exception
DECLARE
P_USERID VARCHAR2(400) DEFAULT NULL;
P_APPLICATION_ID NUMBER DEFAULT NULL;
P_REGISTERED VARCHAR2(400) DEFAULT NULL;
BEGIN
SELECT DISTINCT(USERID) INTO P_USERID FROM ACL_EMPLOYEES
WHERE  USERID = :P39_USERID AND APPLICATION_ID = :APP_ID ;
:P39_TYPE_UTILISATEUR := 'USER_REGISTERED';
EXCEPTION
WHEN NO_DATA_FOUND THEN
:P39_TYPE_UTILISATEUR := 'USER_NOT_FOUND';
END;I would like to do first this statement :
SELECT DISTINCT(USERID) INTO P_USERID FROM ACL_EMPLOYEES
WHERE  USERID = :P39_USERID Then to do this one if the user is found :
SELECT DISTINCT(USERID) INTO P_USERID FROM ACL_EMPLOYEES
WHERE  USERID = :P39_USERID AND APPLICATION_ID = :APP_ID ;etc...
I basically don't want to go to the not found exception before having tested the 4 possibilities.
Do you have a suggestion ?
Thank you for your kind help !
Christian

Answer 1

Surely there are only 3 conditions to check?
1. The user exists and has that app
2. The user exists and doesn't have that app
3. The user doesn't exist
You could do this in one sql statement like:
with mimic_data_table as (select 1 userid, 1 appid from dual union all
                          select 1 userid, 2 appid from dual union all
                          select 2 userid, 1 appid from dual),
-- end of mimicking your table
         params_table as (select :p_userid userid, :p_appid appid from dual)
select pt.userid,
       pt.appid,
       decode(min(case when dt.userid = pt.userid and dt.appid = pt.appid then 1
                       when dt.userid = pt.userid then 2
                       else 3
                  end), 1, 'User and app exist',
                        2, 'User exists but not for this app',
                        3, 'User doesn''t exist') user_app_check
from   mimic_data_table dt,
       params_table pt
where  pt.userid = dt.userid (+)
group by pt.userid, pt.appid;
:p_userid = 1
:p_appid = 2
    USERID      APPID USER_APP_CHECK                 
         1          2 User and app exist   
:p_userid = 1
:p_appid = 3
    USERID      APPID USER_APP_CHECK                 
         1          3 User exists but not for this app
:p_userid = 3
:p_appid = 2
    USERID      APPID USER_APP_CHECK                 
         3          2 User doesn't exist