$($i$)$ Suppose the same database instance as above and SQL statements shown below: UPDATE Catalog SET cost $=$ cost $*0\mathrm{.}95$ WHERE sid $=31$

UPDATE Catalog SET cost $=$ cost $*0\mathrm{.}95$ WHERE sid $=31$

When we use READ COMMITTED on the SQL statements above, an unrepeatable read could occur resulting in an incorrect value being assigned to cost$.$ But this problem cannot occur when we use REPEATABLE READ.

Suppose the same database instance as above and SQL statements shown below $($assuming READ UNCOMMITTED can write to the database$)$:

UPDATE Catalog SET cost $=$ cost $*0\mathrm{.}95$ SELECT C$.$sid, C$.$pid FROM Catalog C WHERE C$.$cost $=36\mathrm{.}22$

When we use READ UNCOMMITTED on the SQL statements above, dirty read of the value of cost could occur because the first SQL statement might not be finished while the second one is reading. But this problem cannot occur when we use READ UNCOMMITTED.