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relation algebra

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Consider a relation R(A, B) that contains r tuples, and a relation S(B, C) that contains s tuples; assume r > 0 and s > 0. Make no assumptions about keys. For the following relational algebra expression, in terms of r and s the minimum and maximum number of tuples that could be in the result?

in Databases 229 views
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$r$ max

$0$ min

1 Answer

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case 1: if in R(a,b) and S(b,c) we have the same values of b then the inner parenthesis evaluates to 0 and then r-0=r(no of tuples in relation r)

case 2: if in R(a,b) and S(b,c) we have no tuple common so the inner bracket gives us r no of tuples and r-r=0

So max=r and min=0
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