Tagged: Tuple

Solving a relational query: part 4


As Paul Rubin pointed out the SQL in the last post was broken – here’s some that, I think (please do not let it be wrong a second time!), by relying on SQL’s coercion of a tuple to a scalar, would work (Paul proposed an even more ambitions way of doing this in a single join):

SELECT DISTINCT U.NAME, U.EMAIL
FROM USER U, BID B, LOT L
WHERE U.USER_ID = B.BIDDER_ID AND
B.AMOUNT > 100 AND B.LOT_ID = L.LOT_ID
AND (SELECT COUNT(*) FROM
BID, LOT WHERE
BID.LOT_ID = B.LOT_ID AND BID.BIDDER_ID = U.USER_ID
AND BID.LOT_ID = LOT.LOT_ID) > 1

Still no clue as to how to do this with relational algebra though.

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Solving a relational query: part 2


Tuple Image from [www.youvan.com], Example 7 i...

Image via Wikipedia

With thanks to Professor Paul A. Rubin, I think this may be the way to solve this:

Relational algebra formula
This joins LOT to a relation with one attribute (LOT_ID) made up from tuples where LOT_ID should only be returned where no bids have been made that are equal or greater than the reserve price.

Very difficult part question for an exam, though :(

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