made-easy mock test2

Question

Answer 1

Answer is 2.

Q1. select the sid of those suppliers who supply all blue parts so we can interpret this query like this

                         ∏_sid(catalog) - ∏_sid ( ∏_sid(catalog x σ_{color = blue}(parts)) - catalog).
which gives all tuples. 

Q2. 0 tuple selected because natural join with null set gives you null and second part gives you null.

Q3.Again 0 tuple selected.

Comments

Here also the solution given by them say that Q1 will return all the tuples as something divides by zero returns all tuples. I don't know though.

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Ok just found out by running the code in mariadb, that Q1 will return all the rows and Q2, Q3 will return zero rows.

That means answer given by madeasy is correct although mock test 2 had many answers given wrongly.

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yup thanks to clear me i also checked it with

∏_sid(catalog) - ∏_sid ( ∏_sid(catalog x σ_{color = blue}(parts)) - catalog).

it also gives all tuples