Consider a database with the following schema:
Suppliers(sid: integer, sname: string, address: string)
Parts(pid: integer, pname: string, color: string)
Catalog(sid: integer, pid: integer, cost: real)
The Catalog relation lists the prices charged for parts by Suppliers.
Consider the transactions T1 and T2. T1 always has SQL isolation level SERIALIZABLE.
We first run T 1 concurrently with T2 and then we run T 1 concurrently with T 2 but we change the isolation level of T 2 as specified below. Give a database instance and SQL statements for T1 and T 2 such that result of running T 2 with the first SQL isolation level is different from running T 2 with the second SQL isolation level. Also specify the common schedule of T1 and T 2 and explain why the results are different.
1. SERIALIZABLE versus REPEATABLE READ.
2. REPEATABLE READ versus READ COMMITTED.
3. READ COMMITTED versus READ UNCOMMITTED.