Perform a LEFT JOIN and check for NULL in the WHERE clause. That should be quite different.
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EXCEPT or MINUS in mysql
Hello,
I got a bunch of questions on mysql, and answered all of them but one. I know asking to solve homework is against this forums rules, so I only ask for a VERY SMALL hint.
And here is the question:
Use the following schema tables:
* City (zip, name, state)
* Customer (cno, title, firstname, name, zip, address)
* Hotel (hno, name, zip, address)
* Room (hno, type, totalrooms, price)
* Reservation (rno, cno, hno, type, arrival, departure)
Question: Which customers have no reservations? (give two alternative to write the SQL sentence).
Writing one was preety easy:
SELECT C.cno
FROM Customer C
WHERE C.cno <> ALL(SELECT R2.cno FROM Reservation R2);
The other option I found is chaning "<> ALL" to "NOT IN", but I think there must be something more different than this one.
I wanted to use EXCEPT or MINUS, but neither of them is implemented in MySQL.
Please give me a small hint.
Thanks!
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Answers
Here's the documentation on rewriting subqueries using outer joins:
http://dev.mysql.com/doc/r
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by: snoyes_jwPosted on 2005-12-01 at 12:50:00ID: 15399747
LEFT JOIN, IS NULL