Relation algebra Query

Question

Consider the following relation and instance of relation:

Supply(sid,Sname)  #sid is key

Parts(pid,Pname,Pcolor)  #pid is the key

Catalog(sid,pid)  #sid,pid is the key

Number of tuples returned by the above Query is ……...

Comments

6?

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Mine was 6 too but its 0

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I think 100,null  on comparing with 100,5 will return false in SQL but not sure in RA. Maybe we have treat it the same here as well

Answer 1

Answer is 0. Bcoz no violet color in parts table.

(In cross product if any one of the table contains 0  record then no tuples will be selected.)

Comments

According to truthtable of subtraction

A	B	A-B
0	0	0
0	1	1
1	0	1
1	1	0

So,we will get 6 values.

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what method is this? Can u explain?

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@bhargav1 Dont post whatever u want