Oracle Join View - which rowid is used

Question

Hi,

CREATE VIEW EVENT_LOCATION ("EVENT_ID", "STREET", "TOWN") AS
  SELECT A.EVENT_ID, A.STREET, A.TOWN
  FROM TBLEVENTLOCATION A
  JOIN TBLEVENTS B
  ON A.EVENT_ID = B.EVENT_ID
  WHERE B.REGION = 'South';

if I run

SELECT ROWID, STREET, TOWN FROM EVENT_LOCATION 

then which ROWID should I get back?

Reason I'm asking is: In the database there are many views with the above 'pattern'. It seems to differ which rowid is being returned from different views. ie. I am getting both A.ROWID or B.ROWID ...

UPDATE: I have resolved this using the following view. Which essentially guarantees the ROWID comes from the right table. Thanks for your replies!

CREATE VIEW EVENT_LOCATION ("EVENT_ID", "STREET", "TOWN") AS
  SELECT A.EVENT_ID, A.STREET, A.TOWN
  FROM TBLEVENTLOCATION A
  WHERE A.EVENT_ID IN (SELECT EVENT_ID FROM TBLEVENTS WHERE REGION = 'South');

Answer 1

Since you get ORA-01445 if non of the tables you use are key-preserving I think it will return the rowid of one of the key-preserving tables. I don't know what will happen if several tables are key-preserving.

Answer 2

Try looking at

select * from user_updatable_columns where table_name = 'EVENT_LOCATION'

The columns that are updatable should indicate the table (and hence the rowid) which Oracle says is the child.

Bear in mind that, if you use multi-table clusters (not common, but possible), then different tables in the same cluster can have records with the same ROWID.

Personally, I'd recommend (a) don't use ROWID in your code anywhere and (b) if you do, then include an explicit evt.rowid evt_rowid column in the view.