Database course

5. Consider a relation R(x) containing integers. Suppose Alice runs a transaction that is a query: select sum (x) from R; select sum (x) from R; commit Bob's transaction is a sequence of inserts: insert into R values (100) insert into R values (200) insert into R values (300) commit; Before any of these transactions execute, the sum of the integers in R is 1000. Alice's and Bob's, transactions run at about the same time. Which of the following sums could be returned by Alice's transaction if the two transactions run under isolation level (i) READ UNCOMMITTED, (ii) READ COMMITTTED, and (iii) REPEATABLE READ