Oracle (day 3)

Time:2021-4-30
1、 Delete: a DML statement. Delete the data with specified conditions in the database
Delete from table name where a = B( Conditional deletion)
Delete from table name; Delete the data of all rows. You cannot delete the value of a column.
After executing the statement, you need to commit to reflect it in the database.
 2、 There are four characteristics of transaction
1. Atomicity: all operations in the transaction are indivisible in the database, either complete or not complete.
2. Consistency: the results of several transactions executed in parallel must be consistent with those executed in a certain order.
3. Isolation: transaction execution is not interfered by other transactions, and the intermediate result of transaction execution must be transparent to other transactions
4. Persistence: for any committed transaction, the system must ensure that the changes of the transaction to the database will not be lost, even if the database fails.
 
3、 Livelocks and deadlocks:
 
 

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