Consider the following transactions:
* S: [X := X + 10; Y := Y - 10]
* T: [X := X * 2; Y := Y * 2]
* U: [Y := Y + 10; X := X - 10]
Assuming initial values of X = 15 and Y = 25, serializable schedules of these three transactions can leave the database in various states. Determine all such possible states. Then, identify from the list below, which of the following is a possible state of the database resulting from a serializable execution of S, T and U.
a) X = 30; Y = 40
b) X = 20; Y = 70
c) X = 40; Y = 40
d) X = 15; Y = 25
2. Suppose relation R(a,b,c) has the following tuples: (1,1,3), (1,2,3), (2,1,4), (2,3,5), (2,4,1), (3,2,4), and (3,3,6). Define the view V by:
CREATE VIEW V AS
SELECT a+b AS d, c FROM R;
What is the result of the query:
SELECT d, SUM(c) FROM V
GROUP BY d
HAVING COUNT(*) <> 1;
Identify, from the list below, a tuple in the result.
a) (2,7) b) (6,7) c) (5,11) d) (6,4)