IN in NATURAL JOIN help

Question

SELECT name,telephone
FROM Customer where cid IN
(SELECT cid
FROM Order where oid IN
(SELECT oid
FROM OrderDetal where icode IN
(SELECT icode
FROM item where itemName=’Dry Fish 200g’)));
How can I convert this query to Natural join?
Thanks in Advance

Answer 1

Hi,
You can't do that with NATURAL JOIN.
Forget about NATURAL JOIN.  I've never seen it used outside of a texbook (or on a forum like this) for good reasons.  If you add a column to any table, that may change the results of any NATURAL JOIN involving that table.  You don't want to look at all those queries whenever you condiser adding a new column to a table; you don't even want to keep track of which queries you'd have to look at.
Upon sober reflection, I think it might be possible to do this with NATURAL JOIN, depending on how your tables are designed. I can't tell if it's possible or not without seeing the CREATE TABLE statements for all the tables involved, including unique constraints. If it is possible, it would look like this:
SELECT        c.name, c.telephone
FROM          Customer   c
NATURAL JOIN  Orders     o -- ORDER is not a good table name
NATURAL JOIN  OrderDetal od
NATURAL JOIN  Item  i
WHERE         i.ItemName = 'Dry Fish 200g'
Depending on your data, you may need SELECT DISTINCT.
Message was edited by: FrankKulash
NATURAL JOIN is still a bad idea.