Question

Design of Database System COurse

True or False

1. {(t.lname) | s ∈ Student, s.stuId = t.stuId, t ∉ Graduate_Student, s.major = ‘CS’} is a safe relational calculus expression.

Answer 1

answer=> false

you are use in (t.lname) that not be used becuse that are touple place

i.e

To express the query 'Find the set of all tuples T such that F(T) is true,' we can write:

{T| F(T)}

but you  are in (t.lname) thts wrong

{(t.lname) | s ∈ Student, s.stuId = t.stuId, t ∉ Graduate_Student, s.major = ‘CS’}

right query are :=>

{R | ∃  s∈Student,∃ t∈Teacher(t ∉ Graduate_Student AND s.major = ‘CS’ AND s.stuId = t.stuId) AND s.lname = t.lname }

R is relation on touple  

∃ exist the relation

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