The given solution is :
However, I believe that simply using the following expression should be enough:
Now, the reason why I believe this is mainly because of the fact that the
EMPLOYEE relation holds the tuples which correspond to workers as well as managers. Now, an employee can be either a worker or a manager. So, going by that logic the above expression should be enough.
I wholeheartedly agree with the fact that a given query can be represented through more than one relational algebraic expressions, however doing what the given solution (the bigger one) suggests above is highly redundant.
So to sum it up, is the direction of my thought correct?
Source : Fundamentals of Database Systems by Ramez Elmasri & Shamkant B. Navathe, 6th Edition, Page No. 172 Query 4.