transaction isolation level

1.1.1 If isolation is not considered, some security issues arise.
Isolation: the execution of a transaction should not be interfered by other transactions.
If isolation is not considered (the execution of a transaction is interfered by other transactions), some security problems will arise, mainly in reading data:
l Dirty read: A transaction reads uncommitted data of another transaction, resulting in inconsistent query results
l Non-repeatable read: A transaction reads the update data that has been submitted by another transaction, resulting in inconsistent results of multiple queries.
l Phantom read/phantom read: A transaction reads the insert data that has been submitted by another transaction, resulting in inconsistent results of multiple queries.
1.1.2 Solve these security problems:
Set the isolation level of the transaction:
l read uncommitted: Dirty reads, non-repeatable reads, and virtual reads may occur
l read committed: Avoid dirty reads. But non-repeatable reads and virtual reads may occur
l repeatable read: Avoid dirty reads and non-repeatable reads, but virtual reads may occur.
l serializable: Avoid dirty reads, non-repeatable reads, and virtual reads.