TUPLE CALCULUS

Question

Comments

option c is correct

Answer 1

1.In left outer join we will first match A column of both the realtion .

If A value of Any one tuple from the R tables  doesn't match with A value of any tuple in S table then it will result  (A,B,Null),

here null is in C column.

In the above problem Highlighted part  is simply assigning values to T tuple  when A attribute of R table is equal to A attribute of 

S table.

Now comes the second part when "if for a given tuple of R table there is no tuple at S table such that R[A]=S[A] then we should assign T[A]=R[A] ^T[B]=R[B] ^ T[C]=null"

Hence option C is right choice.

Comments

I feel option c is wrong. It is because in the second part where we need to include tuples in R which didn't match with tuples S, the condition must be R[A] != S[A]. This condition is present in option A. So, option A is right answer.

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Be careful while reading predicates.

Lets take options 

A)Select those (A,B,C) such that A∊R, B∊R,C=NULL ,such that some R.A does not match with some S.A.

B)Select those (A,B,C) such that A∊S, B∊S,C=NULL ,such that some S.A does not match with some R.A.

C)Select those (A,B,C) such that A∊R, B∊R,C=NULL ,such that some R.A does not match with any of S.A .-----Left outer join

D)Select those (A,B,C) such that A∊S, B=NULL,C∊S ,such that some S.A does not match with any of R.A.--------Right outer join