Is it likely to be more efficient to do a join before selecting out the rows required, or to select rows before doing a join? (a) With reference to the Eats, Keeper and Supervision tables shown in the...

Is it likely to be more efficient to do a join before selecting out the rows required, or to select rows before doing a join?

(a) With reference to the Eats, Keeper and Supervision tables shown in the questions for section 17.3, write a sequence of unnested relational algebra operations to find the foods eaten by animals supervised by keepers called Morris.

(b) Write a single, nested relational algebra statement that answers the part (a) query.