Case, Decode or PlSQL

Question

Hello,
I am new to Oracle. I have a, hopefully basic SQL question.
There is sometime four users in my dbs. But, I would like make query where the users below are returned, even if not in db.
1. Bob
2. Jane
3. John
4. Abul
I have rows in db:
ROWS IN DB
Username account status
bob Support Active
Jane Dev Active
John Dev Expired
How I can write query to find all users, if one is missing. Try to get format
Bob's Support account is active
Jane's Dev account is active
John's Dev account is active
Abul is not in db
I try CASE and Decode, but get bad returns.
Pls help.
Tring to learn SQL. Go to class in three weeks.

Answer 1

Hi,
Welcome to the forum!
So you have four special users, each with a name and id number. That sounds like data. Data belongs in tables. You should create a table that has four rows. Then you could use that table to do an outer-join with other tables, such as db.
If you don't have such a table, you can generate a result set on the fly that will serve as a table. The sub-query special_users below is just that:
WITH  special_users  AS
     SELECT  'Abul' AS username  FROM dual  UNION ALL
     SELECT     'BOB'                 FROM dual  UNION ALL
     SELECT     'Jane'                 FROM dual  UNION ALL
     SELECT     'John'                 FROM dual
SELECT     su.username
    ||  CASE
          WHEN  db.username IS NULL
          THEN  ' is not in db'
          ELSE  '''s ' || account
                          || ' account is '
                    || status
         END     AS msg
FROM     special_users     su
LEFT OUTER JOIN          db     ON     db.username     = su.username
;If you do have a real special_users table, then the main query above works;l just skip the WHERE clause (the forst 7 lines) and, the query is:
SELECT     su.username
    ||  CASE
          WHEN  db.username IS NULL
          THEN  ' is not in db'
          ELSE  '''s ' || account
                          || ' account is '
                    || status
         END     AS msg
FROM     special_users     su
LEFT OUTER JOIN          db     ON     db.username     = su.username
;Edited by: Frank Kulash on Sep 28, 2009 3:53 PM
The subject line you chose for this message, "Case, Decode or PlSQL" is very good, and shows the order in which you should try things.
(1) CASE is the general way to handle if-then-else logic in a SQL expression
(2) DECODE (and other specialized features, such as NVL2, which Michaels used) can save you a little typing in special circumstances. Once you have mastered CASE, you can start exploring these other expressions.
(3) PL/SQL is the last resort, used only if there is no good way to do something in SQL.