Transaction Control for database learning and database learning transactions

Transaction Control for database learning and database learning transactions

Transaction Overview:
1. transactions are databasesConcurrency ControlAndRestoration TechnologyBasic Unit;
2. transactions have four features: atomicity, consistency, isolation, and durability;
3. transactions are a collection of database operations and are composed of a group of related SQL statements;
Oracle transaction isolation level:
Oracle Database provides two levels of isolation for transactions.
1,Read commited:
(1) The query operation performed by each firm can only obtain data that has been committed before the query starts (not before the transaction starts.
(2) It can prevent loss of modifications and dirty reads, but cannot prevent repeated reads.
(3) If the data is locked, wait for other transactions to unlock;
2,Serializable:
(1) Each transaction can only see the data submitted before the transaction starts;
(2) Prevents Loss of modifications, dirty reads, and non-repeated reads;
(3) If the data is locked, no wait and an error is returned;
3,Read-only:
(1) Each transaction can only see the data submitted before the transaction starts, and cannot add, delete, modify, or delete the data in the transaction;
You can refer to the Manual for details on how to modify the transaction isolation level;

Oracle transaction processing:
In the Oracle database,Transaction commitThere are two methods:
One way is to execute the commit command;
The other method is that the system automatically submits a specific operation:
When you execute the create, alter, drop, rename, revoke, grant, connect, disconnect, and other commands, the system will automatically submit them.
Transaction rollback:
If you only want to cancel some operations in the transaction, instead of canceling all operations, you can set a storage point within the transaction to divide a large transaction into several components, in this way, the transaction can be rolled back to the specified storage point.
You can use the savepoint statement to set the save point..