I recently came across this question:
Let the following relation schemas be given:
$R=(A,B,C)$
$S=(D,E,F)$
Let relations r(R) and s(S) be given. Give an expression in the tuple relational calculus that is equivalent to the following:
a. $\pi_A(r)$
The solution provided is:
$\{t|\exists q \in r(q[A]=t[A]) \}$
But according to me, the solution should have been:
$\{t|\exists q \in r(t[A]=q[A]) \}$
Can anyone please help me in fiding out where my error is, or whether I am correct??
Thanks in advance.
