One to many relationship question.

Question

Let's say we have table1 and table2
Table1 has ID, and let's say Name for fields.
Table2 has ID, and let's say SSN for fields.
This is not so, but illustrates my points well.
Table2 has many records with the same ID, who just happen to have the same SSN. That would usually be a logical conclusion.
Table1 has only 1 of each ID in it. So you might say that ID is a foreign key in table2, except one problem. I don't think they know what primary keys are here, much less foreign keys.
Anyway, I have to write a query where I get the ID from table1 and need the SSN from table2. That's the only place in this scenario that SSN is.
My question is this - since this is a one to many relationship, yet I only need 1 result, how would I write this using the (+) way of notation? I am using 8i.
Right now, I am doing something like this, using a DISTINCT:
Select DISTINCT t1.ID, t1.Name, t2.SSN
From table1, table2,
Where t1.ID = t2.ID (+);
First of all, is this the correct way of writing it?
And second, I am wondering if, perchance for some error, there were 2 or more SSNs in table2, what would happen then? Would I get a too many rows error?
And if so, how can I trap it and possibly get just the first occurrence of it?
Is that even a sound way of doing it?
Thanks for any thoughts here.

Answer 1

You would need to turn your table2 into an in-line view in order to outer join to it properly. Minimally, something like:
SELECT t1.id, t1.name, t2.ssn
FROM table1 t1,
     (SELECT DISTINCT id, ssn
      FROM table2) t2
WHERE t1.id = t2.id(+)If there may be multiple ssn in t2 for a single id, you will need to determine which one you want to keep and use something like:
SELECT t1.id, t1.name, t2.ssn
FROM table1 t1,
     (SELECT id, ssn
      FROM (SELECT id, ssn,
                   ROW_NUMBER() OVER (PARTITION BY id,
                                      ORDER BY column_that_makes_it_first) rn
            FROM table2)
      WHERE rn = 1) t2
WHERE t1.id = t2.id(+)This should work on 8.1.7.4 Enterprise Edition. If you have a different version, then the analytic function may not work so you would need something more like:
SELECT t1.id, t1.name, t2.ssn
FROM table1 t1,
     (SELECT id, ssn
      FROM (SELECT id, ssn, rownum rn
            FROM (SELECT id, ssn,
                  FROM table2
                  ORDER BY id, column_that_makes_it_first))
      WHERE rn = 1) t2HTH
John