Note: Just answer with TRUE or FALSE. There is no need to explain. Wrong answers will receive $-0\mathrm{.}2$

points each.

$1.$ If X and Y are superkeys of a relation R$,$ then X $\backslash$cup Y is also a superkey of R$.\_\_\_\_\_\_\_\_$

$2.$ If X and Y are superkeys of a relation R$,$ then X $\backslash$cap Y is also a superkey of R$.\_\_\_\_\_\_\_\_\_\_$

$3.$ If an attribute in is a foreign key for R$,$ then R cannot contain two tuples with the same value for that

attribute. $\_\_\_\_\_\_\_$

$4.$ A relation R can have three different primary keys, e$.$g$.$ each of A$,$ B$,$ and C is a primary key in R$($A$,$

B$,$ C$,$ D$).\_\_\_\_\_\_$

$5.$ A relation R can have two different foreign keys, for example each of A and B is a foreign key in

R$($A$,$ B$,$ C$,$ D$).\_\_\_\_\_\_$

$6.$ In SQL$,$ a primary key can only have one attribute. $\_\_\_\_\_$