Using primitive relational algebra operations, describe how to select a maximum value out of a relation of values.

Question

anonymous · Answer

It's not obvious, huh?

anonymous · Answer

yeah i am not sure on this one i will look into it but its a difficult one

anonymous · Answer

Let's consider this relation:

Values
[100]
[ 90 ]
[101]
[200]
[306]
[ 52 ]

describe a procedure using primitive relational algebra operations that will not only get the tuple containing the largest integer out of all the tuples in this relation, but would also work on any relation with the same number of attributes (i.e. 1)

anonymous · Answer

so basically, I want to obtain [306]

anonymous · Answer

Hmmm...
Recursively applying Select > on consecutive elements all the way through the list.

anonymous · Answer

Interesting problem but I have to head to work...

anonymous · Answer

$$Values$$
$$-$$
$$\pi_{v1}(\sigma_{v1<v2}(\rho_{v1,v2}(Values\ \times\ Values)))$$

anonymous · Answer

That looks about right.  You're using less than, though?

anonymous · Answer

So it works? yay

anonymous · Answer

and if I want the minimum, I use >?

anonymous · Answer

I think the other way around.   select v1<v2 should give you all tuples where v1 is < v2.   for max you want it the other way around.

anonymous · Answer

yeah

anonymous · Answer

I just got all the smaller tuples in one single-dimension list, and subtracted it from the original in order to get just the tuple with the largest value in it.