Isolation keeps the transactions of multiple users isolated from each other. Transaction isolation level controls the degree of locking which occurs when selecting data. This is necessary to avoid situations like:

► Lost updates- when two transactions read the same data.

► Dirty read- Occurs when a transaction reads data that has not been updated.

► Non repeatable reads- occur when different results are read multiple times.

► Phantoms- Occurs when row data matches the first time but does not match subsequent times.