Question

8 points Updating views Given two tables Students(sid, name, age) and Enrolled(studid, cid, grade) consider the vi ew V defined as follows: (n, s,c) ← Students(s.n.aJA Enrolled(s.c.9JA g = "B" The view result consists of tuples of the form (name, sid, cid) and suppose (Joe, 8250. 145) is an example tuple in the result. For each of the following update operations on V, describe how they can be translated into operations on Students and/or Enrolled, and any complications involved (a) Insert a new tuple (Mary, 8251, 645) into V (b) Delete tuple t from V

Answer 1

a)it is impossible to insert new tuple into given veiw because the view is composed of columns form two tables.

if you try to insert values to the given view you can get following error

"Connot modify a colunm which maps to a non key-preaserved data"

b) if you delete a tuple from the view corresponding enrolled table is effected.

rows form the enrolled table are deleted because view is based on the condition grade=b.

so, if a tuple is deleted form view then tuple from the enrolled table is deleted.